[babel-plugin] custom module resolution support

[henryqdineen]

What changed / motivation ?

At HubSpot we use a homegrown package manager for frontend packages that is optimized for our (mostly) closed ecosystem. This can present challenges when integrating third-party tooling but, more often than not, the tooling will support a way to configure module resolution.

This PR introduces a "custom" type to the unstable_moduleResolution configuration option that will allow us and others to plug-in our own resolution algorithm without relying on forks or error-prone patch-package patches. When using "custom" module resolution the consumer will need to provide their implementations for filePathResolver(), and getCanonicalFilePath().

I have tested this branch locally and it works for our needs. I am currently using patch-package on top of 0.16.2, although patching bundled code can be tricky and hard to maintain.

Acknowledgments

• The usage of filePathResolver() and getCanonicalFilePath() leaks implementation details, or at least internal function naming, to the public API. If you prefer something more generic please recommend something.
• This change will introduce config values of type function. I wasn't sure if you were intentionally trying to limit the config only static values but I don't see another way.

Omissions

• I skipped updating docs as I don't expect this feature to be widely used. I considered prefixing likeexperimental_crossFileParsing.
• createShortFilename() still has a implicit dependency on node_modules resolution for non-"haste" module resolution. I'm not familiar enough with that part of the codebase but we can add support in the future.

Linked PR/Issues

This seems like it could be useful to resolve/workaround #1282

Pre-flight checklist

• I have read the contributing guidelines
  Contribution Guidelines
• Performed a self-review of my code

[mellyeliu]

Seems reasonable overall. We may want to document the new custom config within https://stylexjs.com/docs/api/configuration/babel-plugin/#unstable_moduleresolution, but that can be done in a followup.