Make default scale value null so that Flutter decides the one to use

[davidmigloz]

If you have an image with different resolution variants:

assets/images/myImage.png
assets/images/2.0x/myImage.png
assets/images/3.0x/myImage.png

At the moment, if you use the generated image() method with the default parameters. Eg:

Assets.images.myImage.image()

It will always use assets/images/myImage.png independently of the pixel ratio of the device. This happens because the default parameter of scale is 1.0:

Image image({
    Key? key,
    AssetBundle? bundle,
    ImageFrameBuilder? frameBuilder,
    ImageErrorWidgetBuilder? errorBuilder,
    String? semanticLabel,
    bool excludeFromSemantics = false,
    double? scale = 1.0, // <-- THIS
    //...
})

To workaround this issue at the moment you always have to set scale to null:

Assets.images.myImage.image(scale: null)

Proposed fix:
I believe the default value of scale should not be 1.0 but null as it is in the Flutter's Image.asset constructor.

[wasabeef]

@davidmigloz

As you said, I'd like to merge this PR.

[davidmigloz]

Perfect!

(Sorry, I closed the ticket by mistake)

[vietstone-ng]

This is nice. How can I use this pr before it get merged and released?

[wasabeef]

@davidmigloz @vietstone-ng
I will release the next version that included until tomorrow.

[wasabeef]

@davidmigloz @vietstone-ng
Hi, just released v4.3.0.