add skvx::{sin,cos,tan}

This lets us get rid of VECTOR_UNARY_FN_VEC.

I don't know exactly what was wrong with VECTOR_UNARY_FN_VEC,
but `color.rgb = color.rgb + a*(sin(6.28*color.rgb)*0.159)` looks
ok to me now when run through the interpreter.

Change-Id: I700398cd55eca1b8e1b3b46858415ecae5585a32
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/286065
Reviewed-by: Florin Malita <fmalita@chromium.org>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
2 files changed