Add support for Field lvalues.

This allows the code generator to compile assignment into struct
fields. However, non-lvalue field-access expressions have not been
implemented yet, so those assignments cannot be read back.
Surprisingly, we do have one test which now passes because it
meets these criteria.

Change-Id: I2bd46469c6b542d2fb41bce135e7cac43281fe3c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/639859
Commit-Queue: Arman Uguray <armansito@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Arman Uguray <armansito@google.com>
3 files changed