glthread: demystify Draw function names

glthread: demystify Draw function names

Since we had the freedom to write our own marshal and unmarshal Draw
functions, we turned it into a mess by doing whatever we want in those
functions. For example, DrawElementsInstancedBaseVertex actually
implemented DrawArraysInstancedBaseInstanceBaseInstance.

Add 4 internal GL functions that pass user buffers through marshal
/unmarshal functions, and clean up the other names to match their
behavior.

The new functions don't need any parameters in their definitions because
we don't call them directly.

Acked-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18199>