AEP-122: make full resource paths always require the domain

[toumorokoshi]

https://aep.dev/122/#full-resource-paths currently recommends that we don't include the full resource path, unless it is ambiguous:

The full resource path should not be used for cross-API references where the owning API is clear; it is only used if a field refers to resources in multiple APIs where ambiguity is possible.

This makes resource paths much less useful, since it does not allow a the simple pattern of using a relative appending strategy for non-qualified domains, and an absolute path otherwise.

Should we make this a should on fully-qualified paths?