This PR closes#12632 by dimming the caption controls in the titlebar
when unfocused. Leaves them intact when in high contrast mode. The color
used is borrowed from PowerToys' unfocused color.
## Validation Steps Performed
Tested by hovering and unhovering in focused and unfocused states, as
well as in high contrast mode. States are consistent and applied
correctly. I did notice that clicking on the titlebar wouldn't put it
into focus unless I also moved my mouse though, but that is also present
in the release branch.
Closes#12632
8d94edd7b0