eslint-parser: ES2020 features

[JLHwung]

Q	A
Fixed Issues?	Fixes #11711
Minor: New Feature?	Yes
Tests Added + Pass?	Yes
Any Dependency Changes?	eslint-visitor-keys is bumped to ^1.3.0 which includes the ChainExpression visitor keys.
License	MIT

This PR adds estree parsing support on the following features:

• optional chaining expression.
• nullish coalescing
• export * ns (credits to @existentialism)

The nullish coalescing is out of the box since ESTree and Babel shares the AST shape. Thus I have enabled test.

The @babel/parser estree plugin now supports parsing optional chaining and export * ns.

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/25849/

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[nicolo-ribaudo]

Can you add some fixtures tests for ChainExpression in @babel/parser?

[kaicataldo]

I don’t think this needs to block this PR, but we should make sure we bump the ESLint peer dep version once optional chaining lands in ESLint core (hopefully the next release).

I also have a PR open to upgrade to ESLint v7, so if we can land that it should be an easy bump :)

[kaicataldo]

ESLint optional chaining PR here.