Replace Formatter<PyFormatContext<'_>> with PyFormatter (#6330)

This is a refactoring to use the type alias in more places. In the
process, I had to fix and run generate.py. There are no functional
changes.

crates/ruff_python_formatter/src/statement/stmt_assign.rs

@@ -50,7 +50,7 @@ struct FormatTargets<'a> {
 }
 
 impl Format<PyFormatContext<'_>> for FormatTargets<'_> {
-    fn fmt(&self, f: &mut Formatter<PyFormatContext<'_>>) -> FormatResult<()> {
+    fn fmt(&self, f: &mut PyFormatter) -> FormatResult<()> {
         if let Some((first, rest)) = self.targets.split_first() {
             let can_omit_parentheses = has_own_parentheses(first);