Injecting foreign stack frames

Language wrappers like [JPype](https://github.com/jpype-project/jpype/discussions/1071#discussioncomment-2835357) and Cython could use first-class support for injecting “foreign” stack frames/traceback entries.

See https://github.com/python/cpython/issues/86784
