[GTK3] Rename colour definitions
Summary:
Colour definitions are now suffixed with _breeze, and public API colours
are now reexported variables.
CCBUG: 417461
Test Plan:
In tandem with D27426, no visual effect should
be noticeable on Breeze GTK.
Other themes should display an improvement:
Before:
After:
Reviewers: Breeze, ngraham
Reviewed By: Breeze, ngraham
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D27425