Use the correct this in __self for JSX elements in arrows

[nicolo-ribaudo]

Q	A
Fixed Issues?	Reported on Twitter
Patch: Bug Fix?	Yes
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

The problem was that we were injecting __self after transpiling arrow functions, and thus it didn't receive the outer this but the one of the new function expression.

This PR fixes the problem by injecting __self and __source in Program:enter.

Probably windows tests will fail because I tried to manually edit them, I'll fix them after CI tells me the necessary updated.

[nicolo-ribaudo]

I merged this test to the one that runs on linux. Also, I made it input/output rather than calling transform in exec.js.

[lunaruan]

Should we also fix the transform-react-jsx-self plugin so that everyone using that also gets the fix?

[hzoo]

awesome, so we are deprecating the standalone plugins now? (although also true it has been that way since the beginning)

edit: yeah was going to ask the same as @lunaruan

[nicolo-ribaudo]

I can prepare another PR for the standalone plugins, but given that they have been proven for years and that they shouldn't be used anymore I don't think that it's worth it 🤷‍♀️

[lunaruan]

__self is used primarily for a string ref deprecation warning that we have recently enabled. We are worried that people will take some time to upgrade to Babel 8.0 and use the new transform. We would like them to be able to get this warning ASAP so that they can work on removing string refs before they are deprecated, so we would prefer that it is also added to the self transform. Is this okay with you?

Thanks again for doing this!