Change the text color when appmenu is selected or hovered

When the mouse hovers the appmenu item, the text color should be inverted to the background
color. Before this commit, the text was still the same color as the "REST" state, making it
difficult to recognize.

(cherry picked from commit 28537cf3)
2 jobs for Plasma/5.24 in 6 minutes and 54 seconds (queued for 1 minute and 47 seconds)