Auto merge of #54088 - matthewjasper:use-reason-in-dlle-errors, r=pnkfelix

[NLL] Suggest let binding

Closes #49821

Also adds an alternative to `explain_why_borrow_contains_point` that allows changing error messages based on the reason that will be given. This will also be useful for #51026, #51169 and maybe further changes to does not live long enough messages.

src/test/ui/lifetimes/borrowck-let-suggestion.nll.stderr

@@ -9,6 +9,7 @@ LL |     //~^ ERROR borrowed value does not live long enough
 LL |     x.use_mut();
    |     - borrow later used here
    |
+   = note: consider using a `let` binding to create a longer lived value
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
 error: aborting due to previous error