SkSL DSL struct support

Change-Id: I68eb7be8e46454d95bb4a6a9743c923d093c9ba2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/368857
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
10 files changed