* Add more flexible image loading API
This adds a new `instantiateImageCodecWithSize` method, which can be
used to decode an image into a size, where the target size isn't known
until the caller is allowed to inspect the image descriptor.
This enables the use case of loading an image whose aspect ratio isn't
known at load time, and which needs to be resized to fit within a
bounding box while also maintaining its original aspect ratio.
https://github.com/flutter/flutter/issues/118543
* Add test
* Fixed test failure
* Update
* Respond to review comments
* Add web implementation
* Fixed typo
* Review comments
Also changed the TargetImageSizeCallback to just take intrinsic
width & height, rather than the full image descriptor.
* Forgot to remove the _SizeOnlyImageDescriptor class - it's no longer needed
* Forgot to update test
2363e70858