NLL diagnostics miss opportunities to suggest "use `&mut Type` here to make mutable"

[pnkfelix]

The following tests rightly suggest under AST borrowck to use a &mut reference in the type, but there is no such suggestion under NLL.

Tests:

• did_you_mean/issue-38147-1.rs
• did_you_mean/issue-38147-2.rs
• did_you_mean/issue-38147-3.rs
• did_you_mean/issue-38147-4.rs
• span/borrowck-call-is-borrow-issue-12224.rs
• span/borrowck-call-method-from-mut-aliasable.rs
• span/borrowck-fn-in-const-b.rs
• span/borrowck-object-mutability.rs
• span/mut-arg-hint.rs

(This list of tests is drawn from an informal paper document that I have been using to keep notes for myself as I work on this...)

[pnkfelix]

I believe this will be addressed by PR #51275 once that is finalized.