Treat floating-point sampler values as state that is baked into the
sampling routine, instead of reading it from memory. This offers more
opportunities for optimizing the generated code.

Bug: b/151957215
Change-Id: If41455dece60307a54d97463e9ad26ed052f2588
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/42588Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>