Added an API for creating RuntimeEffects using the SkSL DSL.

Change-Id: I305016d305455e2b90fe904d8da93cf7735cc38e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/389316
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
28 files changed