Make it easier to traverse the frame stack for third party tools. #100987

Profilers and debuggers need to traverse the frame stack, but the layout of the stack is an internal implementation detail.
However can make some limited promises to make porting tools between Python versions a bit easier.

In order to traverse the stack, the offset of the previous pointer needs to be known. To understand the frame, more information is needed.

@pablogsal
@Yhg1s
expressed interest in this.

Linked PRs

• GH-100987: Refactor _PyInterpreterFrame a bit, to assist generator improvement. #100988
• GH-100987: Don't cache references to the names and consts array in _PyEval_EvalFrameDefault. #102640
• GH-100987: Allow non python frames in frame stack. #103010
• GH-100987: Allow objects other than code objects as the "executable" of an internal frame. #105727