fix(android): stabilize IME composition and deletion handling (#15370)

## Summary
Fix Android editor IME corruption around composition, autocorrect
replay, delete, Enter, and old WebView delete behavior.

## What changed
- Add Android WebView InputConnection wrapper for editor IME handling.
- Route Android delete events through BlockSuite editor input.
- Guard against keyboard autocorrect/composition replay after delete or
space.
- Stabilize delete fallback on older Android/WebView versions.
- Gate IME diagnostic logs behind debug builds.
- Add Android IME fix notes and regression coverage.

## Validation
- Manual Android testing passed.
- `git diff --check upstream/canary...HEAD`

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Bug Fixes**
* Improved Android text editing for Backspace, Delete, Enter, composing
text, and keyboard events.
  * Prevented input methods from targeting the wrong editor area.
* Improved caret-based text handling, focus synchronization, and
composing-session cleanup.

* **Platform Improvements**
* Added a dedicated Android input bridge for smoother IME interactions
and fallback keyboard behavior.
* Improved editor actions, input recovery, and trusted-page validation
for Android communication.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: DarkSky <darksky2048@gmail.com>

blocksuite/affine/rich-text/src/utils.ts

@@ -57,12 +57,14 @@ export function getPrefixText(inlineEditor: InlineEditor) {
   const inlineRange = inlineEditor.getInlineRange();
   if (!inlineRange || inlineRange.length > 0) return '';
 
-  const nearestLineBreakIndex = inlineEditor.yTextString
-    .slice(0, inlineRange.index)
-    .lastIndexOf('\n');
-  const prefixText = inlineEditor.yTextString.slice(
-    nearestLineBreakIndex + 1,
-    inlineRange.index
-  );
-  return prefixText;
+  const maxMarkdownPrefixLength = 512;
+  const prefixStart = Math.max(0, inlineRange.index - maxMarkdownPrefixLength);
+  const yTextString = inlineEditor.yTextString;
+  const prefixWindow = yTextString.slice(prefixStart, inlineRange.index);
+  const nearestLineBreakIndex = prefixWindow.lastIndexOf('\n');
+  if (nearestLineBreakIndex === -1 && prefixStart > 0) return '';
+
+  return nearestLineBreakIndex === -1
+    ? prefixWindow
+    : prefixWindow.slice(nearestLineBreakIndex + 1);
 }