turnip: rework vertex buffers draw state handling

This exploits a HW optimization for when only the size of a draw state is
changed, to make things simpler and more optimal (assuming a well behaved
user which doesn't unecessarily call CmdBindVertexBuffers many times)

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6665>
3 files changed