Overhaul and greatly expand iteminfo tests

This commit is the rebased summation of dozens of major changes and
additions to the iteminfo tests.

The entire approach to testing is now strongly centered around the
iteminfo_parts enum flags, to verify each piece of information in
isolation from the others.

Each test case focuses on a particular info function like `basic_info`
or `combat_info`, even though the top-level `item::info` function is
usually the only one directly invoked.

New tests include:

- armor fit, sizing, and protection
- item volume and weight, stat/skill requirements
- food and medicine info
- gun and gunmod info
- bionic, book, and tool info
- debug and final info