FEATURE REQUEST: File dialogs

[yaccos]

Currently, Shu features two ways of specifying file paths: Manually entering the file path in the path field or dragging the files onto the screen. I find the latter approach to be the far more convenient option, but I would occationally file having a full file dialog. Besides, drapping and dropping does not work for exports. I suggest adding support for the operating's systems file dialog for selecting files for import and export. This could for instance be done through the rdf crate.

[carrascomj]

That crate looks like a good option, since it supports WASM too and it does not depend on an async runtime, which is important for bevy integration.

I'll probably get to work on these features after shu publication, hopefully soon.