added support for interpreting generic SkSL functions

Bug: skia:
Change-Id: I575b91c654393cc6cfedea617852598e8595d5ed
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/209809
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
10 files changed