Add support for Android

[hannobraun]

Broad platform support (at least all major desktop and mobile platforms, as well as the web) is a goal of Fornjot. This issue tracks support for Android. Android is supported by winit and wgpu, so it should be possible to port Fornjot without too much extra effort.

I don't have a vision for mobile support in general, except that it should be possible to show people your models on your phone or tablet. I also don't know if it would be better to add native support, or somehow piggy-back on top of web support (#73). In any case, #71 might be a blocker.

For a start, it would be great to be able to run Fornjot on Android within a development environment, as well as extending the CI build to make sure that support doesn't deteriorate. Once that is achieved, this issue can be closed and more specific follow-up issues can be opened.

I have very little experience with Android development, and personally don't see this as a priority at the moment. Adding https://github.com/hannobraun/Fornjot/labels/help%20wanted, as any Android support will be dependent on contributors driving the effort, at least for now.

Also see #153, which tracks support for iOS.

[hannobraun]

I have opened #1278. Once that pull request is merged, I intend to close this issue and move Android support to the feature wishlist. There doesn't seem to be much appetite for Android support right now, so there's no reason to keep an open issue around, once we have a working build on CI.