AIP-123: Handling of names for nested collections only considers immediate parent

This is for `core::0123::resource-pattern-singular` and `core::0123::resource-pattern-plural`, and how AIP-123 interacts with affordance for nested collections in AIP-122.

I'm not entirely certain whether this is just a linter problem or also needs clarification in [AIP-122](https://google.aip.dev/122). The basic issue is that the handling of nested collections only considers the parent, rather than all ancestors. e.g. if you have a top-level collection `users`, you should be able to shorten the pattern for any descendant resource type starting with `User`.

See #1408 and #1403.