moved SkSL ExpressionStatement's data into IRNode

Change-Id: I11b1662cd58b01fabba75dbbee40267a62c8b420
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/320639
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
10 files changed