glx: misc fixes for Abaqus
DRI3 window back buffer is a client resource, so it's destroyed when context switch drawable for native window.
But some application like Abaqus may leave a dirty back buffer and reuse it when switch back. So add a driconf option for these kind of app to keep the entire GLX drawable for native window.
Could further optimize to only save dirty back buffer drawable, but I don't think it's worth to add more complexity for wired usage case.
The util_vertex_state_cache commit is for avoiding crash when closing Abaqus.