st/mesa: optimize pipe_sampler_view validation

Before, st_get_texture_sampler_view_from_stobj() did a lot of work to
check if the texture parameters matched the sampler view (format,
swizzle, min/max lod, first/last layer, etc).  We did this every time
we validated the texture state.

Now, we use a ctx->Driver.TexParameter() callback and a couple other
checks to proactively release texture views when we know that
view-related parameters have changed.  Then, the validation step is
simplified:
- Search the texture's list of sampler views (just match the context).
- If found, we're done.
- Else, create a new sampler view.

There will never be old, out-of-date sampler views attached to texture
objects that we have to test.

Most apps create textures and set the texture parameters once.  This
make sampler view validation much cheaper for that case.

Note that the old texture/sampler comparison code has been converted
into a set of assertions to verify that the sampler view is in fact
consistent with the texture parameters.  This should help to spot any
potential regressions.

Reviewed-by: Edward O'Callaghan <[email protected]>
Reviewed-by: Nicolai Hähnle <[email protected]>
Reviewed-by: Marek Olšák <[email protected]>

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