[graphite] Update Skia's linear effect SkSL stub to match Android

This brings Skia's testing framework up to date with:

https://googleplex-android-review.git.corp.google.com/c/platform/frameworks/native/+/34345716

Note that this CL won't change anything on the Android side since Android's LinearEffect SkSL was changed long ago.

In reality all this CL does is munge Skia's static set of strings to match the changes to the LinearEffect stub.

These changes are needed, however, to recreate the Pipeline labels in the follow on CL.

Bug: b/465255225
Change-Id: I3246c28b1d6d6c672985701d1aa368e7b2b3f73e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1137936
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Thomas Smith <thomsmit@google.com>