Pre-allocate output contents during autofix application (#2340)

src/source_code/locator.rs

@@ -139,6 +139,14 @@ impl<'a> Locator<'a> {
             &self.contents[inner_end..outer_end],
         )
     }
+
+    pub fn len(&self) -> usize {
+        self.contents.len()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.contents.is_empty()
+    }
 }
 
 #[cfg(test)]