Properly implement Debug for Window and WindowBuilder

[madsmtm]

• Tested on all platforms changed
• Added an entry to CHANGELOG.md 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

[daxpedda]

This actually highlights a couple of problems we currently have:

• The reason why we put SendSyncWrapper on Fullscreen inside of WindowAttributes is because on MacOS it doesn't implement Sync, maybe we should (can we?) fix that. Because at least right now it's exposed as sync even when it shouldn't.
• SendSyncWrapper should actually not implement Debug, because this means the inner type, which isn't actually Send + Sync might get accessed on the wrong thread, e.g. as in WindowAttributes. Same with Clone.
• RawWindowHandle (in WindowBuilder::with_parent()) is fine because it's unsafe anyway.

[daxpedda]

Addressed this in #3303.