mesa: move glMultiDrawArrays to vbo and fix error handling

mesa: move glMultiDrawArrays to vbo and fix error handling

When any count[i] is negative, we must skip all draws.

Moving to vbo makes the subsequent change easier.

v2:
- provide the function in all contexts, including GLES
- adjust validation accordingly to include the xfb check
v3:
- fix mix-up of pre- and post-xfb prim count (Nils Wallménius)

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>