Auto-dim empty display(s) if have multiple displays to extend display lifetimes

[techdebtcreator]

For a multi-display setup, it would be nice to auto-dim unused displays to a defined brightness to increase their lifetime. I'm imagining this could be a general setting (turned off by default). "Unused" could be defined as having no windows overlapping the display boundaries, so if user drags window into a display it will return to its normal brightness.

This proposed enhancement is similar to #2161. The difference is that autodimming for #2161 is triggered by no cursor / active window on a display, but this enhancement would be triggered by no windows (active or inactive) on a display. Perhaps these enhancements could be implemented together since I could see use cases for both.