Android: preserve PDF callback events under Fabric , disable coalescing for shared PDF events

[mavrickdeveloper]

Summary

This change makes Android TopChangeEvent non-coalescible in react-native-pdf.
fixing : #1009

Problem

PdfView.loadComplete(...) and PdfView.onPageChanged(...) both dispatch through the same TopChangeEvent / topChange path.

Under Fabric, TopChangeEvent inherits React Native's default coalescing behavior. Because both callbacks share the same event type for the same view, a later pageChanged event can replace an earlier loadComplete event before JS receives it.

The result is that native Android successfully loads the PDF, but JS sometimes never receives onLoadComplete.

Root cause

• PdfView.java dispatches both loadComplete|... and pageChanged|... through TopChangeEvent
• TopChangeEvent.java always uses the same event name, topChange
• fabric/RNPDFPdfNativeComponent.js exposes one bubbling event prop, onChange
• TopChangeEvent does not override canCoalesce(), so Fabric may merge these events

Fix

Override canCoalesce() in TopChangeEvent and return false.

That preserves both native callbacks in JS without changing the JS API or adding an app-level workaround.

Why this approach

• minimal change
• preserves the current event contract
• fixes the event loss at the library layer
• avoids relying on downstream workarounds such as treating onPageChanged as a substitute for onLoadComplete

Testing

Validated locally with temporary tracing:

• before this change:
  • native emitted loadComplete
  • native emitted pageChanged
  • JS only received pageChanged
• after this change:
  • JS received loadComplete
  • JS then received pageChanged

This also restored the downstream flow that depended on onLoadComplete firing reliably.

Notes

If team prefer, I can also follow this up with a larger refactor that splits these callback types into distinct Fabric/native events.

Fixes #1009