Test and document what happens when a component element is defined as ref twice

[ThaNarie]

Most "common" use case for this scenario is when an element needs controlling from its parent and grandparent (mostly when dealing with wrappers).
In that case, a grandparent will also select the grandchild component (setting ignoreGuard to true in refComponent(s)), and potentially add bindings to it.

Need to test:

• if the component is only initialised once
• if both refs share the same component instance
• what happens when using bindings from both places that DON'T overlap
• what happens when using bindings from both places that DO overlap

And more advanced:

• what happens with component collections, that maybe partly overlap between parents and children

[ThaNarie]

@jspolancor You could already prepare test cases (maybe first as stories if that's easier?) so we can see what happens, and continue to think about potential solutions from there?