Adds hover/pressed luminance variation to flat buttons of modern theme + some other related fixes in both themes. Together with changes in #114162 this closes #112835.

1. Different hover/pressed luminance for flat buttons and bottom panel tabs:

Master	PR

2. Different hover/selected luminance for trees and item lists:

Master	PR

5. Renderer button uses brighter renderer color on hover instead of turning white (both themes):

Master	PR

6. Pressed colored game toolbar button icons dont get tinted with accent color anymore (both themes):

Master	PR

7. Added text highlight on hover to inspector sections as a temporary improvement until sections are rewritten to subclass FoldableContainer, hopefully in 4.7. That will be a good opportunity to explore new designs for inspector sections and solve other issues like visual separation.