Convert internal SkSL to use .eval()

Also update RELEASE_NOTES to describe new syntax.

Change-Id: I2666551b98f80b61ae3a48c92a9e306cdc7242b0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/444735
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
35 files changed