Extracted definition and access to public instances to a separate module in Fabric

[rubennorte]

Summary

The current definition of Instance in Fabric has 2 fields:

• node: reference to the native node in the shadow tree.
• canonical: public instance provided to users via refs + some internal fields needed by Fabric.

We're currently using canonical not only as the public instance, but also to store internal properties that Fabric needs to access in different parts of the codebase. Those properties are, in fact, available through refs as well, which breaks encapsulation.

This PR splits that into 2 separate fields, leaving the definition of instance as:

• node: reference to the native node in the shadow tree.
• publicInstance: public instance provided to users via refs.
• Rest of internal fields needed by Fabric at the instance level.

This also migrates all the current usages of canonical to use the right property depending on the use case.

To improve encapsulation (and in preparation for the implementation of this proposal to bring some DOM APIs to public instances in React Native), this also moves the creation of and the access to the public instance to separate modules (ReactFabricPublicInstance and ReactFabricPublicInstanceUtils). In a following diff, that module will be moved into the react-native repository and we'll access it through ReactNativePrivateInterface.

How did you test this change?

Existing unit tests.
Manually synced the PR in Meta infra and tested in Catalyst + the integration with DevTools. Everything is working normally.

[rubennorte]

This was unused.

[react-sizebot]

Comparing: d1ad984...a51ca5f

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	156.70 kB	156.70 kB	=	49.58 kB	49.58 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	158.70 kB	158.70 kB	=	50.25 kB	50.25 kB
facebook-www/ReactDOM-prod.classic.js	=	538.92 kB	538.92 kB	=	95.86 kB	95.86 kB
facebook-www/ReactDOM-prod.modern.js	=	522.78 kB	522.78 kB	=	93.55 kB	93.55 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
react-native/shims/ReactNativeTypes.js	+1.43%	7.65 kB	7.76 kB	+2.06%	2.09 kB	2.13 kB
react-native/implementations/ReactFabric-prod.js	+0.43%	311.46 kB	312.79 kB	+0.70%	54.95 kB	55.33 kB
react-native/implementations/ReactFabric-profiling.js	+0.41%	330.79 kB	332.16 kB	+0.59%	58.13 kB	58.48 kB
react-native/implementations/ReactFabric-prod.fb.js	+0.41%	322.16 kB	323.48 kB	+0.65%	56.97 kB	57.34 kB
react-native/implementations/ReactFabric-profiling.fb.js	+0.39%	349.34 kB	350.71 kB	+0.54%	61.13 kB	61.47 kB
react-native/implementations/ReactFabric-dev.js	+0.34%	832.24 kB	835.03 kB	+0.38%	179.59 kB	180.27 kB
react-native/implementations/ReactFabric-dev.fb.js	+0.32%	869.08 kB	871.87 kB	+0.42%	186.70 kB	187.48 kB
react-native/implementations/ReactNativeRenderer-dev.js	+0.25%	845.37 kB	847.49 kB	+0.25%	183.41 kB	183.86 kB
react-native/implementations/ReactNativeRenderer-dev.fb.js	+0.24%	882.19 kB	884.32 kB	+0.24%	190.61 kB	191.06 kB

Generated by 🚫 dangerJS against a51ca5f

[rubennorte]

This definition is also present in ReactNativePublicCompat but we're going to move this module to the react-native repository and we need the definition there as well.

[rubennorte]

This definition was incorrect, as we were using the built-in definition for DOM nodes from Flow.

[javache]

Where is internalInstanceHandle actually used?

[javache]

Could we structure this as the following instead, to create a single shared object between instances?

  // Reference to the shadow node.
  node: Node,
  canonical: {
    nativeTag: number,
    viewConfig: ViewConfig,
    currentProps: Props,
    // Exposed through refs.
    publicInstance: ReactFabricHostComponent,
},

[rubennorte]

I was just implementing that when I saw that comment. Making sure I'm updating all the references using this PR as well, hehe. Thanks!