vbo/dlist: avoid splitting draw commands in multiple draws

vbo/dlist: avoid splitting draw commands in multiple draws

For (Multi)DrawArrays and (Multi)DrawElements commands, the storage size
needed are known early so we can make sure that the prim_store/vertex_store
will be big enough to store the whole command.

This reduces the amount of drawcalls in snx03 tests. For instance in test10:

      | Num draw calls |     GPU-load    |
------|----------------|-----------------|
      | Before | After |  Before | After |
------|--------|-------|---------|-------|
test10|  35k   |   8k  |   58%   |  80%  |

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7078>