Quick fix to declare an unresolved lifetime

[matklad]

With inband lifetimes going away (rust-lang/rust#44524), I believe we should just fix the ergonomics at the ide layer.

Typing fn foo(&'a str) should emit an error for unresolved 'a, and a quick fix to declare a lifetime: fn foo<'a>(&'a str).

See how NoSuchField diagnostics is treated, which has a similar flow with a fix: https://github.com/rust-analyzer/rust-analyzer/search?q=NoSuchField.

@Veykril I believe you did name resolution for lifetimes, could you add a code link for where it is happening?

[Veykril]

Since we don't use lifetimes in type inference and such yet we only actually resolve them in the ide layer(through Semantics).

So I guess we should first actually lower/resolve them in type inference(without using them afterwards, we can just keep the static lifetime hack) and then emit diagnostics from there which I think should happen somewhere around here? https://github.com/rust-analyzer/rust-analyzer/blob/master/crates/hir_ty/src/lower.rs#L162-L351