Set --crate-type cdylib from the cmdline

[Firestar99]

Instead of cargo build, you can use cargo rustc --crate-type dylib to specify the crate type you want the target crate (not it's dependencies) to be compiled to. All "main apk" crates can (but don't have to) remove the previously required declaration in Cargo.toml below:

[lib]
crate-type = ["dylib"]

This is entirely untested due to me not having the Android SDK installed, hoping that github actions will test it properly.

Also see rust-gpu's PR doing the exact same thing, where our Android build failed since I removed the explicit crate type everywhere.

[MarijnS95]

See also prior art in #28, where this was already tried and eventually rejected.

We can always re-evaluate, but it's worthwhile to at least have previous context linked and taken into account.