Add support for installing the formatter directly through cargo

[njs-guy]

The rust package manager has a feature where you can publish binaries to crates.io and install them through cargo. Like you could run cargo install starship --locked and it would install the Starship shell prompt and add it to the path. It seems a lot more convenient than downloading the binary and manually adding it to the path. You can also clone the source code and install it through cargo that way, but having a command that you can copy-paste if you already have Rust installed would be pretty nice.

The pre-built binaries should still be there as an option, but the current installation process seems a little convoluted is all.

[fstxz]

We can't do that right now, unfortunately, because we are using git dependencies (i.e. versions that aren't released yet. Specifically, topiary-core and tree-sitter-gdscript).

[njs-guy]

Ah. That's unfortunate. Definitely something to consider later, though.

[fstxz]

Yeah, I am in favor of this. Publishing to crates.io is quite easy, we should do this once we can.