moved SkSL Field data into IRNode

Change-Id: Ib119035466a9d5dbd870e5b4e22f45f3b56455c4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/321120
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
36 files changed