Use NodePath#hub as part of the paths cache key

[nicolo-ribaudo]

Q	A
Fixed Issues?	Fixes #6437
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

This fixes #6437, implementing option 2. I solved the problem of "we call traverse with no hub" by adding support for traversing a node visiting also the top-level node itself, so that we can directly traverse the Program NodePath that already has the hub.

We might want to, at some point, expose that top-level traversal as an official API, such as NodePath#traverseSelf, but I'm intentionally keeping it under the radar now (even if technically the new capability is accessible from the third-party code).

I don't know if this fixes or not #12570, because it looks like that issue has already been fixed on main?

cc @robhogan this fixes the underlying issue of facebook/metro#906

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/54782/

[nicolo-ribaudo]

I'm very confused by the "old Babel" e2e failure. That test is using @babel/core and @babel/traverse 7.0.0, so I do not see how this patch can affect it 🤔

EDIT: The unit test was actually using both old and new at the same time, and there are some problems with mixing traverse versions. Fixed by #14794.

[liuxingbaoyu]

Would it be better for us to use || instead of ?? in this PR?

[Tofandel]

Posting this here to save some headaches to others

If anyone gets the error

Cannot read properties of undefined (reading 'addHelper')
    at Scope.toArray (@babel/traverse/lib/scope/index.js:464:36)
    at getSpreadLiteral (@babel/plugin-transform-spread/lib/index.js:21:20)

When building after upgrading babel from 7.22.6 to 7.22.7

Make sure to switch from @babel/plugin-proposal-object-rest-spread to @babel/plugin-transform-object-rest-spread in your package json