keyboard: fix interactive dismiss race conditions, rewrite example

Fix several race conditions in the iOS interactive dismiss flow:
- Don't skip keyboard close notifications during pan tracking, which
  left Dart unaware the keyboard was dismissed
- Guard resignFirstResponder with generation check so reopened keyboards
  aren't killed by stale dismiss completions
- Block pan tracking from starting during an in-flight dismiss animation
- Always reset keyboard view bounds when the keyboard opens, not just
  when the dismiss animator is still running
- Handle duration=0 keyboard notifications by snapping immediately
- Gate adaptive learning debug output behind kDebugMode

Rewrite the example as a chat UI demonstrating ListenableBuilder,
scroll freeze during interactive dismiss, and proper bottom inset
handling with max(keyboardHeight, safeBottom).

Modernize example Android project from v1 to v2 embedding with
current AGP/Gradle versions.

example/ios/Runner/Info.plist

@@ -41,5 +41,9 @@
 	</array>
 	<key>UIViewControllerBasedStatusBarAppearance</key>
 	<false/>
+	<key>CADisableMinimumFrameDurationOnPhone</key>
+	<true/>
+	<key>UIApplicationSupportsIndirectInputEvents</key>
+	<true/>
 </dict>
 </plist>