[platforms/drm] Rewrite rotation rendering to use MapTexture
Summary:
The previous code uses a fixed version of GSLS which does not match our suported GL targets. We need both, using kwin's existing MapTexture framework we can achieve the same thing in a better way with less code.
Test Plan:
Had some slight issues with the rotation, but everything appeared the same
as when I applied the patchset with the custom shader.
Reviewers: KWin, zzag
Reviewed By: KWin, zzag
Subscribers: kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D26371