Adds the `crossOrigin` property to the `<img>` tag used for decoding. This allows us to use cross-origin images in CanvasKit as if it were loaded from the same origin, as long as the CORS headers are properly set on the server hosting the image.
In the case where the image doesn't have proper CORS headers, this change causes an error to occur while attempting to decode, rather than later on in Skia when the image is converted into a texture. Hitting the cross-origin error later causes Skia to behave in undefined ways.
Progress towards https://github.com/flutter/flutter/issues/149843
[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style
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