Previously, we were using `PostThreadMessage` to pass messages to
`WindowsPlatform`. This PR switches to an approach similar to `winit`
which using a hidden window as the message window (I guess that’s why
winit uses a hidden window?). The difference is that this PR creates it
as a message-only window.

Thanks to @reflectronic for the original PR #37255, this implementation
just fits better with the current code style.


Release Notes:

- N/A

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Co-authored-by: reflectronic <john-tur@outlook.com>