Make SkPixmap-variant of createBackendTexture public

Change-Id: I51d916d2410428113e29d2fc374e5f1f7f4010b9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/244676
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
15 files changed