windows: Remove the use of `DispatcherQueue` and fix `FileSaveDialog` unresponsive issue (#17946)

Closes #17069, closes #12410


With the help of @kennykerr (Creator of C++/WinRT and the crate
`windows-rs`, Engineer on the Windows team at Microsoft) and @riverar
(Windows Development expert), we discovered that this bug only occurs
when an IME with a candidate window, such as Microsoft Pinyin IME, is
active. In this case, the `FileSaveDialog` becomes unresponsive—while
the dialog itself appears to be functioning, it doesn't accept any mouse
or keyboard input.

After a period of debugging and testing, I found that this issue only
arises when using `DispatcherQueue` to dispatch runnables on the UI
thread. After @kennykerr’s further investigation, Kenny identified that
this is a bug with `DispatcherQueue`, and he recommended to avoid using
`DispatcherQueue`. Given the uncertainty about whether Microsoft will
address this bug in the foreseeable future, I have removed the use of
`DispatcherQueue`.

Co-authored-by: Kenny <kenny@kennykerr.ca>

Release Notes:

- N/A

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Co-authored-by: Kenny <kenny@kennykerr.ca>