Update collections from CPython, fix tests for UserDict/List/String

Clean implementation of changes in PR RustPython#3371 based on feedback.

Copies from [CPython tag `v3.9.7` and adds back custom RustPython changes where needed for:
- `Lib/collections/__init__.py`
- `Lib/test/test_collections.py`

Closes: RustPython#3371

Author: chrismoradi