expose direct methods for decoding to an image

These are meant to contrast MakeFromEncoded(), and emphasize that it is deferred/cached,
while the new methods are not.

Change-Id: I83ac22394cb14cdc84ff8507a514bf708734b84f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/234476
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Reed <reed@google.com>
4 files changed