Make color initialization version of createBackendTexture public

Mechanical.

Change-Id: I48be78a12684fc5243ee509e391984daa190fb7d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/218182
Reviewed-by: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
24 files changed