[skif] Make AutoSurface a member type of FilterResult

This refactor will allow AutoSurface access to private types of
FilterResult to help it participate in pixel boundary trackinga nd
padding.

Bug: b/323886079
Change-Id: I659cf92d0481c625acc6a7dc51344c1e3e7bb124
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/812236
Reviewed-by: James Godfrey-Kittle <jamesgk@google.com>
Auto-Submit: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: James Godfrey-Kittle <jamesgk@google.com>
2 files changed