mesa: shrink size of gl_array_attributes (v2)

mesa: shrink size of gl_array_attributes (v2)

Inspired by Marek's earlier patch, but even smaller.  Sort fields from
largest to smallest.  Use bitfields for more fields (sometimes with an
extra bit for MSVC).  Reduce Stride field to GLshort.

Note that some fields cannot be bitfields because they're accessed via
pointers (such as for glEnableClientState(GL_VERTEX_ARRAY) to set the
Enabled field).

Reduces size from 48 to 24 bytes.
Also reduces size of gl_vertex_array_object from 3632 to 2864 bytes.

And add some assertions in init_array().

v2: use s/GLuint/unsigned/, improve commit comments.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>