Insert empty line between suite and alternative branch after def/class (#12294)

When there is a function or class definition at the end of a suite
followed by the beginning of an alternative block, we have to insert a
single empty line between them.

In the if-else-statement example below, we insert an empty line after
the `foo` in the if-block, but none after the else-block `foo`, since in
the latter case the enclosing suite already adds empty lines.

```python
if sys.version_info >= (3, 10):
    def foo():
        return "new"
else:
    def foo():
        return "old"
class Bar:
    pass
```

To do so, we track whether the current suite is the last one in the
current statement with a new option on the suite kind.

Fixes #12199

---------

Co-authored-by: Micha Reiser <micha@reiser.io>

crates/ruff_python_formatter/src/statement/stmt_match.rs

@@ -48,6 +48,7 @@ impl FormatNodeRule<StmtMatch> for FormatStmtMatch {
         let mut last_case = first;
 
         for case in cases_iter {
+            let last_suite_in_statement = Some(case) == cases.last();
             write!(
                 f,
                 [block_indent(&format_args!(
@@ -55,7 +56,7 @@ impl FormatNodeRule<StmtMatch> for FormatStmtMatch {
                         comments.leading(case),
                         last_case.body.last(),
                     ),
-                    case.format()
+                    case.format().with_options(last_suite_in_statement)
                 ))]
             )?;
             last_case = case;