Test distributions for conformant composition support

[negz]

Description of your changes

Addresses the core functionality touched on in https://github.com/crossplane/conformance/issues/9, plus a bunch of other fiddling and refactoring since I'm still feeling out how these tests should work.

I have:

• [x] Read and followed conformance's contribution process.
• [x] Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

I've run it against a clean Crossplane 1.2.1 install on a kind 1.20.x cluster.