Add Task as a built-in module/type

[smores56]

This change moves the Task opaque IO type from platform-specific implementations to the standard library of Roc. This PR is ready for review, barring final testing by building a pre-release of basic-cli using the twin basic-cli PR. The high level changes are:

• Copied the Task module from the basic-cli platform to crates/compiler/builtins/roc/Task.roc
• Consolidated Task and Effect into just the Task opaque type with definition Task ok err := {} -> Result ok err, which is the old type for Effect a : {} -> a that Task ok err : Effect (Result ok err) wrapped
• Removed the Effect generation code, as everything should use Task directly
  • This includes the generates Effect with [after, map, ...] clause of the hosted module header, which is a breaking change
  • FFI definitions on the host side need to return RocResults now, and FFI type declarations on the Roc side need to always have Task return types
  • Removed generation of the Effect.after, Effect.map, etc. functions as they were needed to glue Effect to Task, but are no longer needed now that those types have been combined
• Renamed hosted modules that contain FFI Roc declarations from Effect.roc to PlatformTask.roc to distinguish their behavior from the old approach and to give a name more descriptive of the new behavior
• Updated almost of the testing, but until basic-cli works, that is on hold

[lukewilliamboswell]

It looks like there is a genuine issue with the False interpreter.

(nix:nix-shell-env) 192-168-1-103:false-interpreter luke$ roc build False.roc
🔨 Rebuilding platform...
0 errors and 0 warnings found in 940 ms
 while successfully building:

    False
(nix:nix-shell-env) 192-168-1-103:false-interpreter luke$ ./False examples/sqrt.false
Ran into problem:
examples/sqrt.false

[ageron]

Task.sequence runs tasks in reverse order, please see roc-lang/basic-cli#235

[Anton-4]

TODO: rename Task.seq to Task.sequence. This was a recent change.

[Anton-4]

TODO from Richard:

I suspect this will be a lot faster by doing appends while building it up and then doing one reverse at the end