Fixed DSL handling of struct field modifiers

This fixes an issue where the field modifiers were incorrectly applied
and adds proper error detection to the modifiers.

Change-Id: I8cd88d3a459df81250c267e6007bca9663b7eda4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/443237
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
3 files changed