Rename ES2 error tests from 'C' through 'G'  to .rts.

A few tests received minor tweaks to make them Runtime Effect-friendly.

Bug: skia:13042
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Arman Uguray <armansito@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Change-Id: I7734390c9fadb53bd74b7b395df611db935fcc0b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/524098
Reviewed-by: Derek Sollenberger <djsollen@google.com>
21 files changed