Transformation should generate default viewBox property based on SVG width/height

[dcorbin]

Googling around, there are numerous people that want the image to scale up to the full size of the parent view. One such example is this StackOverflow request:
https://stackoverflow.com/questions/61657859/how-to-find-correct-values-for-width-height-and-viewbox-with-react-native-svg/61792447#61792447

They key to the solution provided in that link is viewBox. You need to set the viewBox based on the original documents coordinate system. I found this to be the solution for my usage as well.

The problem is, this requires you to manually code these values, and now your Javascript/Typescript is duplicating information that is in the source .SVG. Edit's the source .SVG may break it.

One possibility is to default viewBox to be '0 0 ${width} ${height}` where width and height come from the SVG file. A less appealing but related solution would be to also export some of the SVG data in a Metadata object:

{ height: 90, width: 90}

I am not an SVG expert, and maybe these properties are not always there and maybe there are some SVGs for which this is insufficient, but I think it would improve things by default for many users.