Fix #285, migrate to TypeScript

[stil]

This PR migrates the code to TypeScript.

I kept Babel for compilation to keep it small.

There were a couple of type mismatches that I believe are bugs:

• https://github.com/theKashey/react-focus-lock/blob/master/src/Trap.js#L169 - moveFocusInside returns void?
• https://github.com/theKashey/react-focus-lock/blob/master/src/Lock.js#L141 - this call does not fit signature of useMergeRefs.

Type declarations coming from focus-lock need fixing too (focusSolver can accept arrays):

diff --git a/node_modules/focus-lock/dist/es5/moveFocusInside.d.ts b/node_modules/focus-lock/dist/es5/moveFocusInside.d.ts
index 2f28995..b173bfe 100644
--- a/node_modules/focus-lock/dist/es5/moveFocusInside.d.ts
+++ b/node_modules/focus-lock/dist/es5/moveFocusInside.d.ts
@@ -13,5 +13,5 @@ interface FocusLockFocusOptions {
  * HTML markers (see {@link import('./constants').FOCUS_AUTO} constants) can control autofocus
  * @see {@link focusSolver} for the same functionality without autofocus
  */
-export declare const moveFocusInside: (topNode: HTMLElement, lastNode: Element, options?: FocusLockFocusOptions) => void;
+export declare const moveFocusInside: (topNode: HTMLElement | HTMLElement[], lastNode: Element | null, options?: FocusLockFocusOptions) => void;
 export {};
diff --git a/node_modules/focus-lock/dist/es5/sibling.d.ts b/node_modules/focus-lock/dist/es5/sibling.d.ts
index d318b13..4a02d0f 100644
--- a/node_modules/focus-lock/dist/es5/sibling.d.ts
+++ b/node_modules/focus-lock/dist/es5/sibling.d.ts
@@ -42,13 +42,13 @@ interface FocusNextOptions {
  * @param fromElement - common parent to scope active element search or tab cycle order
  * @param {FocusNextOptions} [options] - focus options
  */
-export declare const focusNextElement: (fromElement: Element, options?: FocusNextOptions) => void;
+export declare const focusNextElement: (fromElement: Element | null, options?: FocusNextOptions) => void;
 /**
  * focuses prev element in the tab order
  * @param fromElement - common parent to scope active element search or tab cycle order
  * @param {FocusNextOptions} [options] - focus options
  */
-export declare const focusPrevElement: (fromElement: Element, options?: FocusNextOptions) => void;
+export declare const focusPrevElement: (fromElement: Element | null, options?: FocusNextOptions) => void;
 declare type FocusBoundaryOptions = Pick<FocusNextOptions, 'focusOptions' | 'onlyTabbable'>;
 /**
  * focuses first element in the tab-order

Anyway, in the current state it requires some minor polishing but I leave it to you to verify.
Hopefully it saves you some work and could speed up introducing TS.

[theKashey]

Thanks, this definitely can save me heaps of time

[stale]

This issue has been marked as "stale" because there has been no activity for 2 months. If you have any new information or would like to continue the discussion, please feel free to do so. If this issue got buried among other tasks, maybe this message will reignite the conversation. Otherwise, this issue will be closed in 7 days. Thank you for your contributions so far.

[stil]

This is still relevant.

[theKashey]

Please dont worry about conflicts.