gh-127833: Fix grammar snippet formatting for help() output by encukou · Pull Request #129692 · python/cpython

encukou

Change pydoc_data to show the "input" of grammar snippet
directives, which is formatted the way we want.

A known issue is cross-grammar links, like those in
the string format specification mini-language, which render
as reST source:

element_index:     `~python-grammar:digit`+ | `index_string`

I don't see a good way to fix this before Sphinx is refactored.