Brightness OSD is not visible on dummy screen when it is being mirrored to a real screen

[waydabber]

In this scenario the brightness controls affect the real screen, however the contents of the dummy screen is presented to the user so the OSD should be visible on the dummy screen.

[waydabber]

There appears to be a regression with this as it is once again not working well.

[waydabber]

I added a super convoluted logic that should handle various scenarios of brightness control when mirroring and streaming is happening and there is an overlay based screen involved. There are scenarios when brightness control simply won't work as expected, but it has hard technical limitations (for example a config when at least mirror member requires overlay based dimming will not work if it is a mirror target or if a mirror source has overly while mirror targets use other methdos - that could lead to double dimming - etc).