Adwaita: Avoid directly coloring labels wherever possible (GTK4)

Directly coloring labels can create a lot of unintended behaviors. Unfortunately we can't avoid directly coloring label:disabled because it can be used individually. This, however, tries to inherit color from the parent element of labels wherever possible.

Fixes #1643 (closed)

Before/After:

This also fixes the button's label color on the selected row;

and also fixes the modelbutton's label color when an app has .devel class (only happened in gtk4):