sidekick: Resource ID heuristic misses some RPCs

We have discovered and documented [some RPCs where resource IDs are not available](https://docs.google.com/document/d/1b-vLKvkYWSgdaqeNUb3rg9SGiyxhj0TOPHh4jFP5bp0/edit?resourcekey=0-3dHsMEyYQ4Ww9qC-0OYboA&tab=t.0) with the current implementation of Resource ID detection (from the resource_reference attribute or using a heuristic.)

We should review these and see if we need to improve our handling or improve the source API.

Draft implementation in https://github.com/googleapis/librarian/pull/5299

Start by reviewing the linked document listing RPCs without available resource IDs and the draft implementation in googleapis/librarian#5299. Compare those cases with the current Resource ID detection behavior, then document or implement the agreed handling, including whether the source API needs improvement.

Written by the indexing model from the issue text.