GLX: fix context render type queries

Querying the GLX_RENDER_TYPE of a GLX context via glXQueryContext will
currently return the render type of the context's FB config, which is
a bitmask of GLX_RGBA_BIT / GLX_COLOR_INDEX_BIT / ... values. However,
this query should really return the render type that was specified
when creating the context, which is one of GLX_RGBA_TYPE /
GLX_COLOR_INDEX_TYPE / .... To enable this, save the render type when
creating a new context (defaulting to GLX_RGBA_TYPE if unspecified),
and then include this value in the context attributes sent to clients.
4 jobs for master in 8 minutes and 55 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Docker Image
passed #5828865
debian-buster

00:04:41

 
  Build And Test
passed #5828866
autotools

00:04:14

passed #5828867
meson

00:02:05

passed #5828868
meson-noglamor

00:01:26