Expose more info in SkCodec::FrameInfo

Bug: b/160984428

Add more fields to SkCodec::FrameInfo, which describes the properties of
an individual frame in an animated image. This allows a client that
wishes to seek to determine frame dependencies so that they can decode
an arbitrary frame, which in turn will allow SkCodec to remove
SkCodec::FrameInfo::fRequiredFrame. Currently, SkCodec seeks through the
stream to determine frame dependencies, but this is unnecessary work
(and storage) for a client that does not want to seek.

These fields also support the proposed APIs in go/animated-ndk.

Move SkCodecAnimation::Blend from SkCodecAnimationPriv (and delete that
file) into SkCodecAnimation.h. Rename its values to be more clear.

Merge common code for populating SkCodec::FrameInfo.

Add a test for a GIF with offsets outside the range of the image. Note
that libwebp rejects such an image.

Update libgifcodec.

Change-Id: Ie27e0531e7d62eaae153eccb3105bf2121b5aac4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/339857
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Reviewed-by: Nigel Tao <nigeltao@google.com>
diff --git a/RELEASE_NOTES.txt b/RELEASE_NOTES.txt
index 3dc29b4..c2b4bbd 100644
--- a/RELEASE_NOTES.txt
+++ b/RELEASE_NOTES.txt
@@ -6,6 +6,9 @@
 
 Milestone 89
 ------------
+  * Expose more info in SkCodec::FrameInfo
+    https://review.skia.org/339857
+
   * Added dither control to the SkImageFilters::Shader factory.
     https://review.skia.org/338156