Document scale parameter for Image and RawImage

[RamonFarizel]

This PR documents the scale parameter for Image and RawImage.
It adds the quote from the Image.memory for other constructors like: Image.asset, Image.new, Image.network, Image.file and RawImage

The scale argument specifies the linear scale factor for drawing this image at its intended size and applies to both the width and the height. For example, if this is 2.0, it means that there are four image pixels for every one logical pixel, and the image's actual width and height (as given by the dart:ui.Image.width and dart:ui.Image.height properties) are double the height and width that should be used when painting the image (e.g. in the arguments given to Canvas.drawImage).

#148623

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• I followed the breaking change policy and added Data Driven Fixes where supported.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[nate-thegrate]

Thanks for improving the documentation here.

Could you also add this explanation to the RawImage.scale field?

  /// The linear scale factor for drawing this image at its intended size.
  ///
  /// The scale factor applies to the width and the height.
  ///
  /// {@macro flutter.painting.imageInfo.scale}
  final double scale;

[RamonFarizel]

Thanks for improving the documentation here.

Could you also add this explanation to the RawImage.scale field?

  /// The linear scale factor for drawing this image at its intended size.
  ///
  /// The scale factor applies to the width and the height.
  ///
  /// {@macro flutter.painting.imageInfo.scale}
  final double scale;

Sure!

[nate-thegrate]

LGTM, thanks for doing this!

[goderbauer]

LGTM