Raw string formatting should not remove quote escape backslahes

Currently, `print(r"\"" + "|" + r"\"''")` gets formatted as `print(r'"' + "|" + r"\"''")`, but raw strings keep the backslash so they not equivalent:

```
> print(r"\"" + "|" + r"\"''")
\"|\"''
> print(r'"' + "|" + r"\"''")
"|\"''
```