Add ENTRY_POINT env.

[lepture]

Related issues:

1. Add more entry points #1084
2. Support index.web.js entry file #3941
3. Support index.jsx entry file #3052

With this change, you can build different bundles via:

ENTRY_POINT=src/admin react-scripts build
ENTRY_POINT=src/shop react-scripts build
ENTRY_POINT=src/blog react-scripts build

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[wwilsman]

This is exactly what we need to get CRA working with acceptance testing. We need a way to bundle the tests using the same bundler that bundles the app. Currently there is no way to do that in CRA without ejecting which is not very ideal.

[stale]

This pull request has been automatically marked as stale because it has not had any recent activity. It will be closed in 5 days if no further activity occurs.

[lepture]

? No activity?

[stale]

This pull request has been automatically marked as stale because it has not had any recent activity. It will be closed in 5 days if no further activity occurs.

[stale]

This pull request has been automatically closed because it has not had any recent activity. If you have a question or comment, please open a new issue. Thank you for your contribution!

[lepture]

WTF.