Add presubmit to generate error if private API is used in named fiddles

The goal is to only demonstrate APIs that we want clients to actually
use.

Change-Id: I450f2596955d789528a514f03f420f07d0177c66
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/642276
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Ravi Mistry <rmistry@google.com>
1 file changed