Create custom resolver and utils package for out-of-tree platforms

[thymikee]

Summary:

Creates a new internal package exposing custom Metro resolver for OOT platforms, leveraging custom resolver options through ?resolver.platformExtension query param in RCTBundleURLProvider.mm.

Example usage:

// metro.config.js
const {getPlatformResolver} = require('@callstack/out-of-tree-platforms');
module.exports = {
  // ...
  resolver: {
    resolveRequest: getPlatformResolver({
      platformNameMap: [{visionos: '@callstack/react-native-visionos'}],
    }),
  }
}

Changelog:

[GENERAL] [ADDED] - Create custom resolver and utils package for out-of-tree platforms

Test Plan:

TBD

[matthargett]

can RNTesterList be shallow-rendered (or similar) using react-native-testing-library so a basic assertion can be made that it resolved the visionOS variant instead of the base iOS version? Or, is there a cheaper way to add a test that pins the behavior? OOT platform stuff has regressed quite a few times in the past due to regressions in RN, Metro, etc, so basic pinning at the integration level is probably a good idea.

[thymikee]

Since resolver is on Metro level + configured through RN CLI config (react-native.config.js), Jest test won't properly catch regressions on a unit level as it would need a lot of mocking. I think a visionOS-specific entry-point would serve as a nice e2e test in this scenario.

[douglowder]

This seems like a very large PR... for easier consumption by other out of tree platforms, it would be nice to have a separate PR for the Metro changes. Is that possible?

[thymikee]

@douglowder yes definitely. We already see a lot of overlap with #34, which indicates changes that should be separated.

EDIT: PR pending here: facebook#41659

[thymikee]

Let's wait for facebook#41697 and bring platform back to react-native.config.js

[okwasniewski]

Let's point to fork repo

[okwasniewski]

Suggested change

	platformNameMap: [{visionos: '@callstack/react-native-vision'}],
	platformNameMap: [{visionos: '@callstack/react-native-visionos'}],

[thymikee]

Good catch :D

[okwasniewski]

So sourceExts would be up to the user to configure?

[okwasniewski]

Let's use lowercase visionOS