impl. _clamp_8888 shaders using general mechanism

This should result in roughly the same binary at
the same speed but with less duplication of code.

The idea is that we take all the runtime configurable
fields and make it clear to the compiler that they're
actually constants, and it propagates them through.

Order of operations does change slightly up in the float
code and some operations become FMAs so there are tiny
invisible diffs when we don't hit lowp.

Cq-Include-Trybots: luci.chromium.try:linux-blink-rel
Change-Id: Ic9d44207bcad39d0cf96c0b55bd65fb61997194f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249054
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed