Implement assist to add missing lifetime to function

[ThouCheese]

To address #11039

[Veykril]

This should ideally be a quickfix for an unresolved lifetime diagnostic. The origin for the diagnostic to emit would be here

rust-analyzer/crates/hir-ty/src/lower.rs

Line 1380 in 16fd9aa

None => error_lifetime(),

, TyLoweringContext has no infrastructure for reporting diagnostics yet though so we'd need to add that as well, best would probably be via callback (Option<&'lt mut dyn FnMut(DiagnosticType)> or similar, Boxing for prototyping is probably better as that doesn't require fiddling with lifetimes first) that is stored in it and that can be set by the caller when creating a TyLoweringContext.

Ultimately it should make its way into the main diagnostics here

rust-analyzer/crates/hir-ty/src/infer.rs

Line 421 in 16fd9aa

pub diagnostics: Vec<InferenceDiagnostic>,

and then be processed like the rest in there.

Also quoting the linked issue:

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 #18074 will make this easier and less messy (no callbacks), so I'll put this into draft until then