Revert "refresh image shader cs/at logic"

This reverts commit 4311f19158f0386aaefa16cc91a48606e4515d45.

Reason for revert: layout test failures seemingly not having to do with bicubic+clamping+sRGB

Original change's description:
> refresh image shader cs/at logic
> 
> Was working on SkVM versions of these when I noticed the existing
> SkRasterPipeline code wasn't terribly tidy.  The main gist here is that
> we can let SkColorSpaceXformSteps::apply() handle almost all the
> final transformation on the way out of the shader.
> 
> I remain a little puzzled why I got a few significant diffs when I tried
> leaving the A8 color unpremul, letting the steps handle matching the
> alpha types instead of me manually with SkRasterPipeline::premul.  For
> now I've left that as-is.
> 
> Similarly I think we could transform that A8 color ahead of time rather
> than doing that over and over at runtime.  This is something I've left
> as a TODO, largely because I don't care enough about coloring A8 to
> investigate right now.
> 
> I've inlined all the logic of explaining src-is-normalized into this
> shader (which is its only user).  That makes it clearer that we can
> always set that bit when bicubic sampling, since we're clamping anyway.
> This causes some invisible diffs when switching to the optimized sRGB
> transfer function stages, which we may or may not be able to get away
> with without guarding...
> 
> Change-Id: Ie6670c6ca5c69958f41aac88324341a10eb3bee1
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/261763
> Reviewed-by: Brian Osman <brianosman@google.com>
> Commit-Queue: Mike Klein <mtklein@google.com>

TBR=mtklein@google.com,brianosman@google.com,reed@google.com

Change-Id: I9c414cb751d9e51219b18dc3d4f54c92d06664ce
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/261815
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
2 files changed