Clean up definitions around transforms on root SVG element

[boggydigital]

Splitting SVG part of w3c/csswg-drafts#894

What part of the SVG spec needs to be cleared up?

• Somewhere it should state that the SVG root element is a CSS layout
  box for the purposes of transformations. Probably in the same place where
  we state that backgrounds, borders, and other properties apply on the root
  element.

• In the SVG view spec (linking chapter), it should state that an
  svgView transformation applies in the same way as a transformation on the
  root element.

• In the SVG view spec, it should clarify whether the transformation

  • is in addition to the transformation defined in the SVG file (e.g.,
    take whatever would normally be drawn, and transform it)
  • OR, a replacement for it, as if it was an !important style override
    (all the other svgView parameters override values specified in
    the SVG file)

[boggydigital]

Not blocking updated 2.0 CR publication - assigning 2.0 Recommendation milestone to clean this up before 2.0 REC

[AmeliaBR]

While working on #56, I realized that we never finished this. I also realized that it's even more complicated than I previously thought, because currentScale/currentTranslate need to factor in, too.

Demo/test case: https://bronze-soup.glitch.me/

[AmeliaBR]

Another thing to be included in this discussion: the implicit transformations created by vector-effect values.