Inject Rust into nonterminal types

[AzureMarker]

Idea: take something like

Comma<T>: Vec<T> {
    // ...
}

and inject Rust into the type using something like:

type __intellij_lalrpop_Comma<T> = Vec<T>;

[dnbln]

Does the name really matter? If not I think it would be a better idea to inject that for all type_refs(except where they are recursive)

[AzureMarker]

I don't think the name of the type alias matters, but it probably should be different enough that it won't be referenced by the user. Also, each injection site should be independent of each other, so names shouldn't clash anyways.

That's a good idea, injecting for all non-recursive type_refs.

[dnbln]

There's one small catch here:

Nonterminal<Rule>: Box<Rule> = {/*...*/};

Trying to rename "Rule" from the injection leads to