macOS: Emit resize on frame_did_change

[sshock]

• Fixes On macOS the frame size could change without window resize #2191
• Fixes downstream Mouse text selection issue with multiple windows alacritty/alacritty#5876

• Tested on all platforms changed
• Added an entry to CHANGELOG.md if knowledge of this change could be valuable to users
• (n/a) Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• (n/a) Created or updated an example program if it would help users understand this functionality
• (n/a) Updated feature matrix, if new features were added or implemented

For testing:

• First make sure "Prefer tabs" is set to "always" in macOS system preferences
  • (so new windows will get grouped as tabs).
• Add a debug statements such as println!("emitting resize event with size = {:?}", size);
  • Add to emit_resize_event method in src/platform_impl/macos/window_delegate.rs.
  • Add to frame_did_change method in src/platform_impl/macos/view.rs. (next to new code)
• Run the multiwindow example program.
  • Each time you hit a key to create a new window, note that the last resize event emitted has the correct size.

[kchibisov]

You should also add a changelog entry for that change.

[sshock]

You should also add a changelog entry for that change.

Done!