Add ImageToColorSpace helper in SkImageFilter

Share this logic among a couple filters that need it. This also fixes a
bug that showed up in the morhpology GM for GPU color space configs.

Re-land of https://skia-review.googlesource.com/c/6475/

BUG=skia:

Change-Id: If7b8d892cf89fa030bae68bdd3c03118f290f032
Reviewed-on: https://skia-review.googlesource.com/6484
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
4 files changed