mesa/st: add special casing for pointsize constant updating during validate

mesa/st: add special casing for pointsize constant updating during validate

the previous method of using affected_states to trigger constant updates
was ineffectual in the scenario where a ubo pointsize was needed on
the first time a non-precompiled shader was used after being the not-last
vertex stage:

* have vs+gs -> gs precompiles with pointsize lowering -> gs constants get updated
* remove gs -> vs was precompiled without pointsize lowering -> vs constants broken

now just do a quick check as in st_atom_shader.c and set the flag manually to
ensure the update is done correctly every time

cc: mesa-stable

fixes #6207

fixes (radv):
KHR-GL46.texture_cube_map_array.image_op_fragment_sh
KHR-GL46.texture_cube_map_array.sampling
KHR-GL46.texture_cube_map_array.texture_size_fragment_sh
KHR-GL46.constant_expressions*

Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15570>