Add a Section to the Language Reference About Runtime Components

[ericsnowcurrently]

Documentation

As I've been working on documentation for using multiple interpreters, I've found that there really isn't any clear explanation of how the Python runtime operates from a high level. In particular I think we'd benefit from having a brief overview of Python's runtime components, both relative to the host and relative to Python's own execution context. To me, the natural place to find this is as a section of the "execution model" page in the language reference.

Linked PRs

• gh-135944: Add a "Runtime Components" Section to the Execution Model Docs #135945