Add support for basic Constant::Str formatting (#3173)

This PR enables us to apply the proper quotation marks, including support for escapes. There are some significant TODOs, especially around implicit concatenations like:

```py
(
  "abc"
  "def"
)
```

Which are represented as a single AST node, which requires us to tokenize _within_ the formatter to identify all the individual string parts.

crates/ruff_python/src/string.rs

@@ -1,6 +1,16 @@
 use once_cell::sync::Lazy;
 use regex::Regex;
 
+/// See: <https://docs.python.org/3/reference/lexical_analysis.html#string-and-bytes-literals>
+pub const TRIPLE_QUOTE_PREFIXES: &[&str] = &[
+    "u\"\"\"", "u'''", "r\"\"\"", "r'''", "U\"\"\"", "U'''", "R\"\"\"", "R'''", "\"\"\"", "'''",
+];
+pub const SINGLE_QUOTE_PREFIXES: &[&str] = &[
+    "u\"", "u'", "r\"", "r'", "u\"", "u'", "r\"", "r'", "U\"", "U'", "R\"", "R'", "\"", "'",
+];
+pub const TRIPLE_QUOTE_SUFFIXES: &[&str] = &["\"\"\"", "'''"];
+pub const SINGLE_QUOTE_SUFFIXES: &[&str] = &["\"", "'"];
+
 pub static STRING_QUOTE_PREFIX_REGEX: Lazy<Regex> =
     Lazy::new(|| Regex::new(r#"^(?i)[urb]*['"](?P<raw>.*)['"]$"#).unwrap());