Usages can be generated with empty `resourceRef.name` fields

### What happened?
The `Usage` creation logic does not check to ensure that the `metadata.name` field is populated and can generate `Usage` resources with empty `resourceRef.name` fields for `of` or `by` or both.

### How can we reproduce it?
This is mostly a problem in testing with `crossplane render` where the observed list of resources may be generated and could be missing the `metadata.name` field.

Using a set of observed resources without the `metadata.name` field set, run `crossplane render` on a composition and observe that the `resourceRef.name` fields are set to '""'

### What environment did it happen in?
Function version: v0.5.0