feat(picture): support sizes attribute

[cawa-93]

Description

Add support for responsive images generated by picture plugin.

1. Width dimension descriptors are provided instead of pixel ratio values (200w instead of 2x for example) if image has sizes attribute.
2. sizes attribute preserved and passed for all sources

Source code:

<img src="img.png" imagick="100@2" sizes="(width < 700px) 100px, 200px"/>

Before this change:

<picture>
	<source srcset="img-100w.png, [email protected] 2x"/>
	<img src="img.png" />
</picture>

After this change:

<picture>
	<source srcset="img-100w.png 100w, [email protected] 200w"  sizes="(width < 700px) 100px, 200px"/>
	<img src="img.png" />
</picture>

Check List

• Have you read the
  CODE OF CONDUCT
• Have you read the document
  CONTRIBUTING
  • One pull request per feature. If you want to do more than one thing,
    send multiple pull request.
  • Write tests.
  • Run deno fmt to fix the code format before commit.
  • Document any change in the CHANGELOG.md.

[oscarotero]

Thank you!