Document the various code generation tools used by CPython

[pxeger]

Describe the enhancement or feature you'd like

There should be some documentation about the various code generation tools used in CPython, for example:

• freeze_modules.py
• deepfreeze.py
• generate_global_objects.py

I don't think there needs to be a massive amount of documentation about these. Just a brief mention of their purposes, how to invoke them, and notes about their related make targets.

Related are the Parser generator etc., which are already documented under Guide to CPython's Parser, but could also be mentioned. I think their existing docs could also be used as something of a template.

Describe alternatives you've considered

Argument clinic is already documented at https://docs.python.org/3/howto/clinic.html so maybe this documentation would be more appropriate in the main Python repo's docs? I'll defer to the devguide maintainers on this.

Additional context

Started from a conversation at python/cpython#30941 (comment)

CC @ericisnowcurrently