Add TextEffect component and registry for custom text span effects (#56720)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/56720

Introduces a generic TextEffect system that lets apps register custom text
span effects without modifying React Native core. This can serve for use cases like `react-native-live-markdown`, or product specific effects.

The implementation is pretty dumb right now. It's just a marker, where we can add some JSON serializable data, to be serialized during Spannable creation on JS side MapBuffer.

**JS API:**
```js
import requireNativeTextEffect from 'react-native/Libraries/Text/requireNativeTextEffect';
const Spoiler = requireNativeTextEffect<{}>('RCTSpoiler');

<Text>Normal <Spoiler>hidden text</Spoiler></Text>
```

**Android registration** (via FabricUIManager):
```kotlin
val fabricUIManager = UIManagerHelper.getUIManager(
    context, UIManagerType.FABRIC) as? FabricUIManager
fabricUIManager?.textEffectRegistry?.register("RCTSpoiler") { props ->
    MyCustomSpan()
}
```

Changelog: [Internal]

Reviewed By: javache

Differential Revision: D98812222

fbshipit-source-id: 7000a0452b7592cdc2b26e7eaa37ec95736efce4