Allow derivatives in Runtime Effects when ES3 restrictions are off.

We can now add functions to sksl_public.sksl with an $es3 prefix. These
will be allowed in a Runtime Effect when strict-ES2 mode is disabled.
Note that the CPU backend still doesn't have support for these calls,
and will fail ungracefully (assertion, nonsense result) if these
intrinsics are used.

The testing here is limited, due to an unrelated bug in SPIR-V
(skia:12340)

Change-Id: I9c911bc2b77f5051e80844607e7fd08ad386ee56
Bug: skia:12202, skia:12340
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/439058
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
16 files changed