Introduce SVG-context-agnostic attribute builders for most common attributes in SVG

[Schahen]

As of one has nothing to do other than writing code as follows:

        Circle(200f, 200f, 0.5f * radius.value, attrs = { attr("fill", rgbColor()) })

While fill, for instance, is a very common attribute used literally almost anywhere in SVG.

[okushnikov]

Please check the following ticket on YouTrack for follow-ups to this issue. GitHub issues will be closed in the coming weeks.