[platforms/virtual] Add support for EGL_MESA_platform_surfaceless

Summary:
Thus we don't require vgem any more which fails with latest mesa.
Kepping the vgem variant as fallback for older systems. See T10245

Test Plan:
SceneOpenGL Test passes without init vgem, not tested with
latest mesa

Reviewers: KWin

Subscribers: kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D17980