Reland "hook up float comparisons to x86 JIT"

This is a reland of 12cea8d6c429d06425be97af31db7c31655e5290

Now implementing float comparisons on ARM also.
Only vaguely tricky thing is that x!=y is ~(x==y).

Original change's description:
> hook up float comparisons to x86 JIT
>
> This gets the draws in gm/skvm.cpp all JITing again,
> and in one of the unit tests.
>
> (Everything draws the same of course.)
>
> Change-Id: Iada28690d9df78f9d444ee3765e21beb29239672
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/253166
> Auto-Submit: Mike Klein <mtklein@google.com>
> Reviewed-by: Mike Klein <mtklein@google.com>
> Commit-Queue: Mike Klein <mtklein@google.com>

Cq-Include-Trybots: skia.primary:Test-Android-Clang-NVIDIA_Shield-CPU-TegraX1-arm64-Debug-All-Android
Change-Id: I771b8a327a958db8a0d509d55863ade935a00035
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/253401
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
3 files changed