Write Rustdoc titles like "x in crate::mod - Rust"
This makes Rustdoc titles for items be like "Widget in cratename::blah::foo - Rust". Titles for modules and other non-items are unchanged, and still read like "cratename::blah::foo - Rust". This makes managing several open Rustdoc tabs easier.

This also adds some tests for the new title behavior.
Closes#84371.