## Summary
This PR implements the `blank_line_after_nested_stub_class` preview
style in the formatter.
The logic is divided into 3 parts:
1. In between preceding and following nodes at top level and nested
suite
2. When there's a trailing comment after the class
3. When there is no following node from (1) which is the case when it's
the last or the only node in a suite
We handle (3) with `FormatLeadingAlternateBranchComments`.
## Test Plan
- Add new test cases and update existing snapshots
- Checked the `typeshed` diff
fixes: #8891