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.