This:

• fixes Split extra help item computing with help record rendering #2516.

This is a small refactor of the original Option.get_help_record() method, splitting it in two to separate the generation of extra items in help screen and their rendering.

This PR:

• extracts from get_help_record() the code responsible for extra items generation, and move it to its own get_help_extra() method
• leaves the original get_help_record() as-is, but rely on the new get_help_extra() method to fetch the extra items to render for the help
• makes the new get_help_extra() returns a dictionary of extra items to be rendered, so get_help_record() can pick them up to render (and translate) them the way it wants
• augments the original get_help_record() unittests to inspect values returned by get_help_extra()

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.