[Feature] Spelunk WinUIEx and integrate things

[codemonkeychris]

Problem

Several core gaps in Window, SysTray, etc., which can easily be addressed by integrating features from an existing open library.

Proposed solution

With @dotMorten's guidance, we should look through https://github.com/dotMorten/WinUIEx and address the gaps here, and eventually integrate into WinUI directly. Ensure proper attribution in 3p license notice, etc.

Alternatives considered

No response

Additional context

No response

Confirmation

• I have searched existing issues and specs for prior discussion of this idea.

[codemonkeychris]

dup with #184