add `__bool__` overloads to `builtins` types

`int`, `str`, `bool`, `tuple`

tuple will be easy, but the `True` overloads on the rest are impossible

The issue names `int`, `str`, `bool`, and `tuple` and requests `__bool__` overloads for these builtins. Start by locating the builtins type definitions and the checker tests for overload behavior; done requires a defined, testable treatment of the stated impossible `True` overloads.

Written by the indexing model from the issue text.