moved SkSL Switch data into IRNode

Change-Id: I0373cccfd3acc56417f8d1545bbe7320dc2dfa05
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/327256
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
16 files changed