make compat lib with reason-react

[jchavarri]

As the upstream reason-react gets updated, it gets hard to track the changes / differences between the APIs. This adds a library where a react.rei interface can be shared with reason-react so both libs stay in sync easily, until we have better support for virtual libraries or other mechanisms.

See companion PR in reason-react: reasonml/reason-react#807.

⚠️ Should not be merged yet ⚠️ this is what the build shows as errors / missing APIs:

$ dune build
File "packages/react/src/js_compat/react.ml", line 1:
Error: The implementation packages/react/src/js_compat/react.ml
       does not match the interface packages/react/src/js_compat/.unused_js_compat.objs/byte/unused_js_compat__React.cmi:
        The type `componentLike' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 2, characters 0-55:
         Expected declaration
       The type `component' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 3, characters 0-55:
         Expected declaration
       The value `component' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 12, characters 0-66:
         Expected declaration
       The value `createElementVariadic' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 18-19, characters 0-56:
         Expected declaration
       The value `jsxKeyed' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 21, characters 0-74:
         Expected declaration
       The value `jsx' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 23, characters 0-47:
         Expected declaration
       The value `jsxs' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 25, characters 0-48:
         Expected declaration
       The value `jsxsKeyed' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 27, characters 0-75:
         Expected declaration
       The value `jsxFragment' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 29, characters 0-25:
         Expected declaration
       The value `memo' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 87, characters 0-48:
         Expected declaration
       The value `memoCustomCompareProps' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 89-90, characters 0-68:
         Expected declaration
       The module `StrictMode' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 98-102, characters 0-1:
         Expected declaration
       The value `useReducerWithMapState' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 135-137, characters 0-27:
         Expected declaration
       The value `useSyncExternalStore' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 139-144, characters 0-11:
         Expected declaration
       The value `useSyncExternalStoreWithServer' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 146-152, characters 0-11:
         Expected declaration
       The value `useEffect' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 154, characters 0-53:
         Expected declaration
       The value `useEffect7' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 171-172, characters 0-70:
         Expected declaration
       The value `useInsertionEffect' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 174, characters 0-62:
         Expected declaration
       The value `useInsertionEffect0' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 176, characters 0-63:
         Expected declaration
       The value `useInsertionEffect1' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 178, characters 0-74:
         Expected declaration
       The value `useInsertionEffect2' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 180, characters 0-73:
         Expected declaration
       The value `useInsertionEffect3' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 182-183, characters 0-54:
         Expected declaration
       The value `useInsertionEffect4' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 185-186, characters 0-58:
         Expected declaration
       The value `useInsertionEffect5' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 188-189, characters 0-62:
         Expected declaration
       The value `useInsertionEffect6' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 191-192, characters 0-66:
         Expected declaration
       The value `useInsertionEffect7' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 194-195, characters 0-70:
         Expected declaration
       The value `useLayoutEffect' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 197, characters 0-59:
         Expected declaration
       The value `useLayoutEffect7' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 216-217, characters 0-70:
         Expected declaration
       The value `useMemo7' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 235, characters 0-66:
         Expected declaration
       The type `callback' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 238, characters 0-50:
         Expected declaration
       The value `useCallback7' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 256, characters 0-60:
         Expected declaration
       The value `useId' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 261, characters 0-25:
         Expected declaration
       The value `useDeferredValue' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 263, characters 0-30:
         Expected declaration
       The value `useImperativeHandle0' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 265-266, characters 0-54:
         Expected declaration
       The value `useImperativeHandle1' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 268-269, characters 0-65:
         Expected declaration
       The value `useImperativeHandle2' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 271-272, characters 0-64:
         Expected declaration
       The value `useImperativeHandle3' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 274-275, characters 0-68:
         Expected declaration
       The value `useImperativeHandle4' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 277-278, characters 0-72:
         Expected declaration
       The value `useImperativeHandle5' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 280-281, characters 0-76:
         Expected declaration
       The value `useImperativeHandle6' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 283-285, characters 0-6:
         Expected declaration
       The value `useImperativeHandle7' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 287-293, characters 0-6:
         Expected declaration
       The module `Uncurried' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 295-334, characters 0-1:
         Expected declaration
       The value `useTransition' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 336, characters 0-71:
         Expected declaration
       The module `Experimental' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 338-341, characters 0-1:
         Expected declaration
       The value `displayName' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 345, characters 0-52:
         Expected declaration
       The value `useDebugValue' is required but not provided
       File "packages/react/src/js_compat/react.rei", line 347, characters 0-70:
         Expected declaration
       The module `Event' is required but not provided
       File "packages/react/src/js_compat/react.rei", lines 349-880, characters 0-1:
         Expected declaration

[jchavarri]

reasonml/reason-react#807 (comment)