Cargo dependency names are parsed as identifiers

[jhaye]

When defining the Rust target with a cargo dependency, that dependency's name is parsed as an identifier. This means that if it contains a keyword, LFC throws a parsing error.

For example, this target config:

target Rust {
    build-type: Release,
    cargo-features: ["cli"],
    cargo-dependencies: {
        cpu-time: "1",
    }
};

Throws the following error:

'time' is a reserved keyword which cannot be used as an identifier.

I'm not familiar with the parser, so I don't know how to fix this.

[cmnrd]

Maybe @lhstrh can comment? But I am afraid that the only real fix for this is not using xtext...

[cmnrd]

I don't know if it works, but one idea could be to use Token instead of ID for the keys.

[lhstrh]

See #1238.