dzn: Add KHR_draw_indirect_count support

dzn: Add KHR_draw_indirect_count support

Unfortunately it's not as simple as passing the indirect draw count
buffer to ExecuteIndirect. The compute job that populate the execute
buffer also needs to know the number of entries that need to be
patched. Instead of transitioning the indirect count buffer from
GENERIC_READ to INDIRECT_ARGUMENT we just keep at as a read-only
resource and copy the draw_count value to the exec buffer in the
compute job.

Acked-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15914>