[web] instantiateImageCodecWithSize hardcodes allowUpscaling: false, breaking ResizeImage(allowUpscaling: true) #195193

Description

In engine/src/flutter/lib/web_ui/lib/painting.dart, instantiateImageCodecWithSize invokes getTargetSize(width, height) (where ResizeImage has already enforced its own allowUpscaling parameter) and then passes a hardcoded allowUpscaling: false to engine.engineInstantiateImageCodec:

final TargetImageSize targetSize = getTargetSize(width, height);
return await engine.engineInstantiateImageCodec(
  buffer._list!,
  targetWidth: targetSize.width,
  targetHeight: targetSize.height,
  allowUpscaling: false,
);

On native (dart:ui), instantiateImageCodecWithSize scales to whatever TargetImageSize is returned by getTargetSize, leaving upscaling policy to the caller (ResizeImage.allowUpscaling). Because the web implementation hardcodes allowUpscaling: false, ResizeImage(..., allowUpscaling: true) clamps target dimensions back down to the intrinsic image size on web.

Note: packages/flutter/test/painting/image_provider_resize_image_test.dart (line 622) still skips its ResizeImage group on isBrowser referencing closed #73120.

Steps to Reproduce

1. Remove skip: isBrowser on line 622 of packages/flutter/test/painting/image_provider_resize_image_test.dart.
2. Run:

   flutter test --platform chrome test/painting/image_provider_resize_image_test.dart

Expected Results

All ResizeImage tests pass on Chrome (both CanvasKit and Skwasm), upscaling images when allowUpscaling: true is specified.

Actual Results

16 allowUpscaling: true test cases fail because the decoded ui.Image remains at its intrinsic dimensions instead of scaling up to the size returned by getTargetSize.