Flow Indexed Access Type support

[gkz]

Q	A
Fixed Issues?
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?	x
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?	No
License	MIT

This adds parsing support for Flow's Indexed Access Type, e.g. type T = Obj['foo']. This feature is similar to the TypeScript feature of the same name.
Flow parser has parsed this feature since 0.146

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/44876/

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit 8001a36:

Sandbox	Source
babel-repl-custom-plugin	Configuration
babel-plugin-multi-config	Configuration

[sosukesuzuki]

Oh, I've already implemented the same feature at #13053 ...

[gkz]

Oh, I've already implemented the same feature at #13053 ...

That's funny, we haven't publicized this feature anywhere yet, not even in the changelog, so it did not cross my mind someone external would have already added support in a non-merged PR.

[sosukesuzuki]

I'm a also maintainer of Prettier so I saw that you created the PR to support this feature to Prettier.

[gkz]

It looks like the only differences in the PRs is that I have split the parser tests into separate sub-directories, otherwise pretty much identical. Since your PR is already accepted and tagged "Ready to be merged" I can close this one.