support lists for exclude option in TOML

python#11329 added support for nicer `exclude` lists

TOML has a built-in list syntax, and it would be nice to use that for specifying lists for the `exclude` option.

This change tries the ini-style first: if `exclude` is set to a multiline string, it will split that on newlines, otherwise it will assume it's a list.

mypy/config_parser.py

@@ -143,6 +143,7 @@ def check_follow_imports(choice: str) -> str:
  'disable_error_code': try_split,
  'enable_error_code': try_split,
  'package_root': try_split,
+ 'exclude': lambda s: [p.strip() for p in (s.split('\n') if isinstance(s, str) else s) if p.strip()],
 })