Add Tree::max_size to compute actual SVG size

[JustForFun88]

This PR adds Tree::max_size to easily get the final rendered size of an SVG, including all strokes, filters, and transforms.

Motivation

This reduces boilerplate for anyone who needs the actual canvas size, for example when computing a scaling Transform to fit the SVG into a target region and to help avoid memory overflows (see #814).

[LaurenzV]

Hmm, I'm not sure I'm convinced that we should have this method, it seems very specific. If anything, we should maybe adapt the documentation of Tree::size that this does not refer to the actual bounding box?

[JustForFun88]

Hmm, I'm not sure I'm convinced that we should have this method, it seems very specific. If anything, we should maybe adapt the documentation of Tree::size that this does not refer to the actual bounding box?

That makes sense. I agree that updating the docs for Tree::size with a note and an example on how to get the actual rendered bounds would definitely help users.

Having a dedicated method like Tree::max_size is not strictly essential, but it does make things more convenient and helps avoid having to think about how to correctly calculate the actual SVG size. But this isn’t very important to me 😆, so I’m happy to go with whatever you think is best for the project

[LaurenzV]

I think updating the docs would be better, yes.

[RazrFalcon]

Why do we need a one-line wrapper?
And even then, just keep the current naming convention, aka abs_layer_bounding_box + copy-paste its docs.