Consolidate logic to extract entity config from entity

Multiple areas of the code need to map from a vertex/edge to a vertex/edge config. This code should all use the same logic to reduce the chance of issues.

* Schema sync when fetching attributes
* Keyword search
* User query
* Neighbor expansion

Locate the implementations for schema sync attribute fetching, keyword search, user query, and neighbor expansion, then compare how each maps a vertex or edge to its config. Consolidate those paths around one shared extraction logic and verify that all four behaviors remain consistent.

Written by the indexing model from the issue text.