Add mipmap support to SkPixmap flavor of createBackendTexture

Change-Id: I7a2dea9b0b8e6b985f2d56e587939266022c19e1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/234664
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
9 files changed