Support custom command / toolchain for rustfmt

[msrd0]

I'd like to be able to use nightly Rust for rustfmt but keep using stable Rust for everything else. Stable rust is set as the default toolchain in rustup and I always call cargo +nightly fmt for code formatting. However, I couldn't find any option in atom-ide-rust to replicate this behaviour. Instead, everytime I save a file this package adds a whole bunch of trailing commas, likely because the option to remove those is unstable and ignored by stable rustfmt.

[Green-Avocado]

Version 1.1.0 should support this by configuring rust-analyzer with rust-analyzer.json

From https://rust-analyzer.github.io/manual.html#configuration :

rust-analyzer.rustfmt.extraArgs (default: [])

• Additional arguments to rustfmt.

rust-analyzer.rustfmt.overrideCommand (default: null)

• Advanced option, fully override the command rust-analyzer uses for formatting.

[aminya]

We can probably add a note to the readme explaining an example

[jon-chuang]

@Green-Avocado rust-analyzer.json does not seem to be loaded. I tried restart all language servers, tested with misformatted json to force an error. It failed to even show any change.

My json:

{
  "cargo.unsetTest": [
    "minitrace"
  ]
}

Edit: turns out when I tried reinstalling my ide-rust package, it did not update to 1.1.1.

It works now that I've made sure it updates.