windows: emit minimize/restore events to keep custom platform view synced

[KaithyRookie]

Connection with issue(s)

Resolve issue #2789

Connected to #2789

Testing and Review Notes

Background

Issue #2789 describes a Windows-specific case where, after minimizing/moving a Flutter app using InAppWebView, desktop interaction can be blocked by an overlay-like stale platform view state.

Root Cause

In flutter_inappwebview_windows, platform view geometry sync was primarily driven by move-related events (WM_MOVING, WM_EXITSIZEMOVE) and app lifecycle callbacks.
Minimize/restore transitions (WM_SIZE with SIZE_MINIMIZED / SIZE_RESTORED / SIZE_MAXIMIZED) were not explicitly emitted through PlatformUtil, so CustomPlatformView could miss position/size resync on those transitions.

What this PR changes

• Add minimize/restore event support in PlatformUtilListener (Dart):
  • onWindowMinimize
  • onWindowRestore
• Emit those events from native Windows layer:
  • WM_SIZE + SIZE_MINIMIZED -> onWindowMinimize (and onWindowMove)
  • WM_SIZE + SIZE_RESTORED/SIZE_MAXIMIZED -> onWindowRestore (and onWindowMove)
• Handle the new events in CustomPlatformView by forcing:
  • _reportSurfaceSize()
  • _reportWidgetPosition()

Files changed

• flutter_inappwebview_windows/windows/platform_util.cpp
• flutter_inappwebview_windows/windows/platform_util.h
• flutter_inappwebview_windows/lib/src/platform_util.dart
• flutter_inappwebview_windows/lib/src/in_app_webview/custom_platform_view.dart

Manual test steps

1. Run the Windows example/app that hosts InAppWebView.
2. Load any regular page (e.g., https://google.com).
3. Minimize the app window.
4. Verify desktop icons remain clickable and no overlay-like blocked region remains.
5. Restore/maximize the app window.
6. Verify WebView remains visible and interactive.
7. Move the window around and verify WebView tracks position correctly.

Regression checks

• Existing move event behavior still works (onWindowMove, onWindowStartMove, onWindowEndMove).
• No API breaking changes (only additive listener methods).
• Windows build succeeds with the new native branch.

Screenshots or Videos

• Before fix:
  https://github.com/user-attachments/assets/e4fdcc32-d8c5-46d0-899a-1a133533748f

• After fix:
  https://github.com/user-attachments/assets/eb141537-cdbe-4eb1-901b-6f9b794881d6