Message 387815 - Python tracker

@BTaskaya, do you think you'll have time to open a PR with your AST validator this weekend? It looks good to me (assuming tests pass).

Also, we should add the AST docs to our documentation to-do list (should be just adding entries for ast.Match, ast.MatchAs, ast.MatchOr, and ast.match_case).

I'll try to find time to review the open doc PRs today.