Add most important intrinsics to the interpreter

Started with component-wise comparison and mix builtins.

Implemented min, max, clamp, and saturate using those.
Moved dot to SkSL as well. Because we now have builtins
implemented using other (intrinsic) builtins, I had to
split the include file in two - this lets the intrinsics
be marked so we can call them from the second phase of
builtins that are written in SkSL.

Given that the comparisons and kSelect are now used by
these, I added vector versions of those instructions.
I also switched the kSelect args to match GLSL mix(),
mostly so the logic of mapping intrinsic arguments to
instruction register args remains simple.

Inspired by the (never-landed):
https://skia-review.googlesource.com/c/skia/+/230739

Change-Id: Iecb0a7e8dc633625ff2cada7fb962bf2137fa881
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/272516
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
8 files changed