Closed requested to merge kusma/virglrenderer:use-arb-framebuffer into master
While reading the source-code of vrend, it kept bothering me that we mix usage of GL_EXT_framebuffer and GL_ARB_framebuffer.
These extensions are virtually the same, and mesa treat them identically. The only real difference between them, is that FBOs are defined to be shared across contexts in GL_EXT_framebuffer, but not in GL_ARB_framebuffer. Most OpenGL desktop-implementations just ignore this detail, and always share them, whereas on mobile some do and some don't.
We don't really care about the semantical difference anyway, as we create new FBOs per context regardless. So let's modernize this code to use the non-suffixed extension always.