The py_reconfig rules work by wrapping: The outer reconfig rule applies a transition, depends
on an inner py base rule, then jumps through various hoops to ensure it looks and acts
like the target it's wrapping.

This is error prone, incomplete, and annoying code to maintain. Phil recently discovered it wasn't properly propagating the output group, so he had to add that. I wasted time trying to fix a bug I thought was in it, but actually was working correctly. The logic within it is a bit hacky as it tries to emulate some of the platform-specific stuff for windows. Every time
py_reconfig gains something to transition on, there's numerous places to define, propagate,
and extract the pieces necessary to do it.

To fix this, make the py_reconfig rules not wrap an inner base py rule. Instead, they use the same underlying rule args that the base rules do. This lets them act directly as the rule they're designed to test.

Customization is done by capturing all the rule args in builder objects. The py_reconfig code constructs the same builder the base rules do, then modifies it as necessary (adding attributes, wrapping the base transition function). As a bonus, this sets some ground work to allow more easily defining derivative rules without having to copy/paste arbitrary parts of how the base rules are defined.

Work towards #1647