Added SkSL DSL switch statements

Change-Id: Iccb6f1bb65dce5b313716dfdf3a4eb87b9bb4fc3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/368058
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
13 files changed