Rollup merge of #86189 - JohnTitor:relate-fn-pub, r=Aaron1011
Rollup merge of #86189 - JohnTitor:relate-fn-pub, r=Aaron1011

Make `relate_type_and_mut` public

#85343 improved diagnostics around `Relate` impls but made `relate_type_and_mut` private, which was accessible as `relate` previously. This makes it public so that we can use it on rust-semverver.

r? ```@Aaron1011```

graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust