moved SkSL Extension data into IRNode

Change-Id: I6689bfc78e407ddd840d81ea56c844da92f3a65a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/320724
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
7 files changed