Custom overlay pause and resume

Use pause() before presenting a custom modal or div over native UI and
resume() when it closes. For Ionic overlays, use the automatic
Ionic integration, which shares this coordination but only
covers surfaces behind the overlay.

Plugin authors: re-export the Engine functions

export { pause, resume } from '@webview-native-ui/engine';

The functions share one pause count across Engine-enabled plugins and bundles in
the same document. No wrapper or native plugin method is needed.

Application authors: pair each pause with a resume

import { pause, resume } from 'your-plugin';

pause();
try {
  await showCustomModal();
} finally {
  resume();
}

showCustomModal() must resolve when the modal closes. With event-driven modals,
call resume() on dismissal, cancellation or failure. Use one pair per overlay,
even with multiple plugins; nested overlays each need their own pair.

A pause replaces visible native surfaces with prepared Web images or their normal
Web fallback. Hidden surfaces stay hidden. The final resume() releases
the request, preserving each plugin's presentation intent and remaining Ionic
overlay coverage.

The counter does not track callers or pair individual calls. An extra resume()
while paused can release another overlay's request; only a resume() at zero has
no effect. Each owner must release exactly once for each pause it requested.

Both functions return immediately, without waiting for native acknowledgments or
painting. Returning from pause() does not mean native UI has already moved
behind the Web overlay; it may remain in front until the handoff completes.
The final resume() defers native restoration until the second animation frame,
allowing overlay removal to paint without guaranteeing compositor completion.
Call it after removing the overlay or completing
its dismissal animation. A new pause() cancels a pending restoration.
Calling pause() just before a blocking window.alert() therefore does
not guarantee a completed handoff. They do not detect custom overlays automatically.