win-dshow: Close device dialogs during shutdown

[prgmitchell]

Description

Prevent OBS from hanging during shutdown by enumerating the DirectShow thread's windows and posting WM_CLOSE to all visible dialogs before waiting for the thread to exit. I did add a window visibility check because I logged every window being closed while testing and saw a bunch of windows that were not visible, not sure if this is necessary and can remove if not.

Motivation and Context

I have just been scrolling through issues looking for ones that seem pretty easy/straight forward to fix.
Fixes #13534

How Has This Been Tested?

Opened the configure video window from a video capture device source, closed the main OBS window which now resulted in the configure video window closing as expected.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have read the contributing document.
• My code has been run through clang-format.
• My code follows the project's style guidelines
• My code is not on the master branch.
• My code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.