## Link to GitHub Issue, if one exists
n/a
## Description of change
Need to filter out system-created windows (such as `CicMarshalWnd`) when
looking up which window to mess with when user interacts with F11 menu.
While I'm here, clean up the hack for gfdm arena model that remembers
the main window.
## Testing
Tested:
DDR
gfdm arena 4 / 1 window modes
iidx (windowed mode, with/without nosub option)
sdvx with sub windows
Need to check:
full screen games
bicarus
cd14ca800e