v2.0.20

Requires Dart sdk: '>=2.19.0'

• Enable combinators_ordering for strict
• Enable use_string_in_part_of_directives
• Enable unreachable_from_main for strict
• Enable dangling_library_doc_comments for strict
• Enable collection_methods_unrelated_type
• Enable implicit_call_tearoffs
• Enable unnecessary_library_directive
• Enable library_annotations