egl: Add GL_MESA_EGL_sync support

This commit follow OES_EGL_sync to universially enable use of EGL sync
objects with desktop OpenGL contexts.

Reviewed-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
22 jobs for !624 with GL_OES_EGL_sync-for-Big-GL in 14 minutes and 43 seconds (queued for 2 seconds)
merge request