This gets rid of the following paths:
* OS_STRING
* TO_OWNED
* TO_STRING
Also removes some usages of:
* PATH_BUF
And the now completely unused `clippy_lints::types::is_ty_param_path`
This makes it possible to pass the `Impl` directly to functions, instead
of having to pass each of the many fields one at a time. It also
simplifies matches in many cases.