When using push constants, we end up having dynamic offsets on the
input parameter of the interpolation functions, so we need to be able
to handle this case. Since this is for push constants, we assume that
all dynamic offsets will be the same, for simplicity.

Bug: b/171415086
Change-Id: I5de1720e383c234c9392421d507a66e6d7ba2445
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/52930
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>
Commit-Queue: Alexis Hétu <sugoi@google.com>