Export option to "bake" use element

[ComplianceFailure]

Feature Description

First off, this is a lovely program. It exposes the SVG spec in a beginner-friendly yet robust way, which has helped me learn a lot and I'd love to see it grow.

I noticed that the 'use' element seems to function properly if added manually. Obviously this drastically speeds up making repetitive designs, but an SVG importer I've been using for my game does not support this feature. (See: https://github.com/SlugFiller/godot-vector2d/tree/godot-4.0)

I reckon this is niche, but it would be nice to convert use elements to duplicates of their source shapes on export.

[MewPurPur]

Nice idea! Putting it on the backburner for when I rework the inspector and can have more specialized editors for each element. This is also when I can add <use> to the GUI