sql/inspect: add INSPECT support for inverted indexes

Currently, INSPECT skips consistency checks on inverted indexes. These indexes differ from regular secondary indexes since a single primary key row can produce multiple inverted entries (one per token or element). To fully support them, INSPECT needs logic to reconstruct and validate token-to-row mappings.

- Define validation semantics for inverted index entries (e.g., per token or per source row).
- Add decoding and comparison support in the index consistency checker.
- Verify correctness using JSON, ARRAY, and spatial inverted index cases.

Jira issue: CRDB-55170

Epic CRDB-55075