Fix ref type compatibility for builtin components

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

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

After this diff, no workaround will be required.

**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).

```diff
  // Before — required workaround
- const ref = useRef<View>(null);
+ const ref = useRef<React.ComponentRef<typeof View>>(null);
  ref.current?.measure(...);

- const inputRef = useRef<TextInput>(null); 
+ 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

Author: huntie

packages/react-native/index.js.flow

@@ -22,17 +22,24 @@
 
 // #region Components
 
+// _HostInstance is mapped to a companion type export for each built-in component,
+// enabling ref type compatibility in TypeScript (e.g. `useRef<View>()`).
+import type {HostInstance as _HostInstance} from './src/private/types/HostInstance';
+
 export type {ActivityIndicatorProps} from './Libraries/Components/ActivityIndicator/ActivityIndicator';
 export {default as ActivityIndicator} from './Libraries/Components/ActivityIndicator/ActivityIndicator';
+export type ActivityIndicator = _HostInstance;
 
 export type {ButtonProps} from './Libraries/Components/Button';
 export {default as Button} from './Libraries/Components/Button';
+export type Button = _HostInstance;
 
 export type {
   DrawerLayoutAndroidProps,
   DrawerSlideEvent,
 } from './Libraries/Components/DrawerAndroid/DrawerLayoutAndroid';
 export {default as DrawerLayoutAndroid} from './Libraries/Components/DrawerAndroid/DrawerLayoutAndroid';
+export type DrawerLayoutAndroid = _HostInstance;
 
 export type {FlatListProps} from './Libraries/Lists/FlatList';
 export {default as FlatList} from './Libraries/Lists/FlatList';
@@ -56,13 +63,17 @@ export type {
   ImageURISource,
 } from './Libraries/Image/ImageSource';
 export {default as Image} from './Libraries/Image/Image';
+export type Image = _HostInstance;
 export {default as ImageBackground} from './Libraries/Image/ImageBackground';
+export type ImageBackground = _HostInstance;
 
 export type {InputAccessoryViewProps} from './Libraries/Components/TextInput/InputAccessoryView';
 export {default as InputAccessoryView} from './Libraries/Components/TextInput/InputAccessoryView';
+export type InputAccessoryView = _HostInstance;
 
 export type {KeyboardAvoidingViewProps} from './Libraries/Components/Keyboard/KeyboardAvoidingView';
 export {default as KeyboardAvoidingView} from './Libraries/Components/Keyboard/KeyboardAvoidingView';
+export type KeyboardAvoidingView = _HostInstance;
 
 export type {LayoutConformanceProps} from './Libraries/Components/LayoutConformance/LayoutConformance';
 export {default as experimental_LayoutConformance} from './Libraries/Components/LayoutConformance/LayoutConformance';
@@ -74,27 +85,33 @@ export type {
   ModalPropsIOS,
 } from './Libraries/Modal/Modal';
 export {default as Modal} from './Libraries/Modal/Modal';
+export type Modal = _HostInstance;
 
 export type {
   PressableAndroidRippleConfig,
   PressableProps,
   PressableStateCallbackType,
 } from './Libraries/Components/Pressable/Pressable';
 export {default as Pressable} from './Libraries/Components/Pressable/Pressable';
+export type Pressable = _HostInstance;
 
 export type {ProgressBarAndroidProps} from './Libraries/Components/ProgressBarAndroid/ProgressBarAndroid';
 export {default as ProgressBarAndroid} from './Libraries/Components/ProgressBarAndroid/ProgressBarAndroid';
+export type ProgressBarAndroid = _HostInstance;
 
 export type {
   RefreshControlProps,
   RefreshControlPropsAndroid,
   RefreshControlPropsIOS,
 } from './Libraries/Components/RefreshControl/RefreshControl';
 export {default as RefreshControl} from './Libraries/Components/RefreshControl/RefreshControl';
+export type RefreshControl = _HostInstance;
 
 export {default as SafeAreaView} from './Libraries/Components/SafeAreaView/SafeAreaView';
+export type SafeAreaView = _HostInstance;
 
 export type {
+  PublicScrollViewInstance as ScrollView,
   ScrollViewImperativeMethods,
   ScrollViewScrollToOptions,
   ScrollResponderType,
@@ -118,15 +135,18 @@ export type {
   StatusBarStyle,
 } from './Libraries/Components/StatusBar/StatusBar';
 export {default as StatusBar} from './Libraries/Components/StatusBar/StatusBar';
+export type StatusBar = _HostInstance;
 
 export type {
   SwitchChangeEvent,
   SwitchProps,
 } from './Libraries/Components/Switch/Switch';
 export {default as Switch} from './Libraries/Components/Switch/Switch';
+export type Switch = _HostInstance;
 
 export type {TextProps} from './Libraries/Text/Text';
 export {default as Text} from './Libraries/Text/Text';
+export type Text = _HostInstance;
 export type {NativeTextProps as unstable_NativeTextProps} from './Libraries/Text/TextNativeComponent';
 export {NativeText as unstable_NativeText} from './Libraries/Text/TextNativeComponent';
 export {default as unstable_TextAncestorContext} from './Libraries/Text/TextAncestorContext';
@@ -151,20 +171,25 @@ export type {
   SubmitBehavior,
 } from './Libraries/Components/TextInput/TextInput';
 export {default as TextInput} from './Libraries/Components/TextInput/TextInput';
+export type {TextInputInstance as TextInput} from './Libraries/Components/TextInput/TextInput.flow';
 
 export {default as Touchable} from './Libraries/Components/Touchable/Touchable';
 
 export type {TouchableHighlightProps} from './Libraries/Components/Touchable/TouchableHighlight';
 export {default as TouchableHighlight} from './Libraries/Components/Touchable/TouchableHighlight';
+export type TouchableHighlight = _HostInstance;
 
 export type {TouchableNativeFeedbackProps} from './Libraries/Components/Touchable/TouchableNativeFeedback';
 export {default as TouchableNativeFeedback} from './Libraries/Components/Touchable/TouchableNativeFeedback';
+export type TouchableNativeFeedback = _HostInstance;
 
 export type {TouchableOpacityProps} from './Libraries/Components/Touchable/TouchableOpacity';
 export {default as TouchableOpacity} from './Libraries/Components/Touchable/TouchableOpacity';
+export type TouchableOpacity = _HostInstance;
 
 export type {TouchableWithoutFeedbackProps} from './Libraries/Components/Touchable/TouchableWithoutFeedback';
 export {default as TouchableWithoutFeedback} from './Libraries/Components/Touchable/TouchableWithoutFeedback';
+export type TouchableWithoutFeedback = _HostInstance;
 
 export type {
   AccessibilityActionEvent,
@@ -182,6 +207,7 @@ export type {
   ViewPropsIOS,
 } from './Libraries/Components/View/ViewPropTypes';
 export {default as View} from './Libraries/Components/View/View';
+export type View = _HostInstance;
 export {default as unstable_NativeView} from './Libraries/Components/View/ViewNativeComponent';
 
 export type {