Auto merge of #45990 - murarth:rc-from-strs, r=alexcrichton
Implement `Rc`/`Arc` conversions for string-like types
Provides the following conversion implementations:
* `From<`{`CString`,`&CStr`}`>` for {`Arc`,`Rc`}`<CStr>`
* `From<`{`OsString`,`&OsStr`}`>` for {`Arc`,`Rc`}`<OsStr>`
* `From<`{`PathBuf`,`&Path`}`>` for {`Arc`,`Rc`}`<Path>`
Closes #45008