React Native: bridge native text measurement for virtualized lists

[fuleinist]

React Native lacks a native text measurement backend, making virtualized lists with Pretext inefficient.

Pretext already has fast, accurate text measurement. Exposing it via a React Native bridge (TurboModule or legacy Bridge) would allow mobile apps to use pre-calculated heights in FlatList/VirtualizedList without JS thread overhead.

This unlocks Pretext for mobile UIs where performance-critical text layouts are common.