Preserve raw string prefix and escapes (#15694)

## Summary

Fixes #9663 and also improves the fixes for
[RUF055](https://docs.astral.sh/ruff/rules/unnecessary-regular-expression/)
since regular expressions are often written as raw strings.

This doesn't include raw f-strings.

## Test Plan

Existing snapshots for RUF055 and PT009, plus a new `Generator` test and
a regression test for the reported `PIE810` issue.

crates/ruff_python_ast/src/str.rs

@@ -24,6 +24,14 @@ impl Quote {
         }
     }
 
+    #[inline]
+    pub const fn as_str(self) -> &'static str {
+        match self {
+            Self::Single => "'",
+            Self::Double => "\"",
+        }
+    }
+
     #[must_use]
     #[inline]
     pub const fn opposite(self) -> Self {