Move SkDebugfStream into SkStreamPriv.

This was buried inside SkVM, but can be useful in other contexts as
well.

Change-Id: If5b7dbca24b5c3fb8d4a4f136421c9ddb2f005d8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/473138
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Herb Derby <herb@google.com>
3 files changed