kcms/colors: Properly apply tinting to the window titlebar

Tint the window titlebars only when either the option to tint all colors with
accent color or the option to apply accent color to window titlebars is enabled 
or both), and in the latter case, the active window titlebars should be painted
in the accent color.

BUG: 455395
BUG: 454047
FIXED-IN: 5.25.3


(cherry picked from commit 00a18a8c)
3 jobs for Plasma/5.25 in 12 minutes and 52 seconds (queued for 4 seconds)