Rollup merge of #145013 - fee1-dead-contrib:push-vwvsqsqnrxqm, r=nnethercote

overhaul `&mut` suggestions in borrowck errors

* This refactors the logic so that it does not use fuzzy string matching for suggestions; it instead uses information directly from MIR.
* If something comes from a custom `Index` impl for which the `IndexMut` trait does not apply, do not suggest adding `mut` after `&`.
* Suggest `get_mut` with `unwrap` if error is fired on `BTreeMap` or `HashMap`.

Supersedes rust-lang/rust#144018 cc ```@xizheyin```
Closes rust-lang/rust#143732

Author: Zalathar