Fix ref type compatibility for builtin components (#56673)

[huntie]

Summary:

Fix useRef and forwardRef backcompat when migrating to React Native's generated TypeScript types (Strict TypeScript API).

Previously this was an awkward breaking change: https://reactnative.dev/docs/strict-typescript-api#some-core-components-are-now-function-components-instead-of-class-components

- const ref = useRef<View>(null);
+ const ref = useRef<React.ComponentRef<typeof View>>(null);

After this diff, no workaround will be required.

Changes

• Add companion type aliases alongside each component's value export.
• Introduces a new /* ts-only */ comment syntax in index.js.flow to hide the companion exports from Flow, which has no equivalent concept of declaration merging.

Problem detail

In our Flow source code, built-in components like View and TextInput are function components rather than classes. This differs from the previous manual .d.ts files which defined each component as a class.

In TypeScript, a class name serves as both a value (the constructor) and a type (the instance), so patterns like useRef<View>() work. However, with function components, the name is only a value (the function signature) making useRef<View>() resolve to a ref holding the function itself, not the native element.

The fix: Add companion type aliases alongside each component's value export. TypeScript's declaration merging makes the component name simultaneously a value (for JSX) and a type (for refs).

export {default as View} from './Libraries/Components/View/View';
export type View = _HostInstance;

  // Before — required workaround
- const ref = useRef<View>(null);          // TS2749: 'View' refers to a value, not a type
+ const ref = useRef<React.ComponentRef<typeof View>>(null);
  ref.current?.measure(...);

- const inputRef = useRef<TextInput>(null); // TS2749: 'TextInput' refers to a value, not a type
+ const inputRef = useRef<React.ComponentRef<typeof TextInput>>(null);
  inputRef.current?.focus();

  // After — original patterns work as-is
  const ref = useRef<View>(null);          // View as a type = HostInstance
  ref.current?.measure(...);               // HostInstance has measure()

  const inputRef = useRef<TextInput>(null); // TextInput as a type = TextInputInstance
  inputRef.current?.focus();               // TextInputInstance has focus()

Changelog:
[General][Fixed] - Add companion instance type aliases for built-in components, preserving useRef<Component> patterns under the Strict TypeScript API

Differential Revision: D103601923

[meta-codesync]

@huntie has exported this pull request. If you are a Meta employee, you can view the originating Diff in D103601923.