embrace raw-window-handle 0.5 and remove WindowHandleWrapper

[sonodima]

Baseview has transitioned to utilizing raw-window-handle 0.5, and this commit eliminates the need for the WindowHandleWrapper.

I haven't updated baseview to its latest commit, but rather to the one prior, because in my tests the changes made to the macOS window cleanup logic in the latest commit caused a BorrowMutError when closing the window in the window_subs example.