Increase thoroughness of Composition conformance tests

### What problem are you facing?

We need to ensure distributions of Crossplane provide conformant support for Composition.

### How could conformance help solve your problem?

We could ~add~ increase the thoroughness of tests for Composition. We should at a minimum test that:

* [x] Well formed XRDs become established and offered when they're installed.
* [x] XRDs define cluster scoped XRs and namespace scoped XRCs.
* [x] Creating an XRC creates a corresponding XR and composes resources per the Composition used.
* [x] XRs and XRCs write their connection secrets as instructed.

We may also want to test that:

* [x] Selecting compositions works as intended.
* [ ] Enforcing and defaulting compositions works as intended.
* [ ] Both anonymous and named composition templates work as intended.
* [ ] All supported patch and transform types work as intended.