fix(helpers): match Reflect.get behaviour

[lightmare]

Q	A
Fixed Issues?	no related issue found
Patch: Bug Fix?	✔️
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	✔️
Documentation PR Link
Any Dependency Changes?
License	MIT

The first call to babelHelpers.get substitutes target for falsy 3rd argument receiver. That is not correct for several reasons:

1. subsequent calls don't do that (because the implementation is invoked directly)
2. a falsy 3rd argument is still a valid receiver
3. Reflect.get step 3. "If receiver is not present, then ... Set receiver to target."

The reimplementation should follow Reflect.get spec, i.e. only substitute target when receiver argument is missing, not when it's falsy or nullish.

Regarding tests, I think I know how to devise a test for the falsy receiver issue, but I have no idea how to test the first-call stub behaviour.

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/49729/

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[nicolo-ribaudo]

To test this you can set "externalHelpers": false in the test options, so that the helper is inlined and you can capture the behavior of the first call.

[lightmare]

Rebased on main, and added 2 tests that fail before the patch, pass after.

[nicolo-ribaudo]

Thanks!