Return error on missing event instead of panicking.

[shanecelis]

Problem: winit would panic when appkit::drag_window() was called without a left click event being present. This problem was discovered while reviewing this PR for bevy.

Solution: Return a result from drag_window(). In winit 0.30.5 drag_window() already returned a result, but 'main' branch had no return value. So this reverts the function signature to an earlier one.

It seems like this affects macOS. I exercised this on an M2 macOS machine using the "window" example.

• [x] Tested on all platforms changed
• [X] Added an entry to the changelog module if knowledge of this change could be valuable to users
• [ ] Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• [ ] Created or updated an example program if it would help users understand this functionality
• [ ] Updated feature matrix, if new features were added or implemented

[kchibisov]

Needs a changelog entry.

[shanecelis]

I added a change log entry under the changed and fixed section. I don't believe the other three unchecked items are necessary for this PR.