examples-resolve tool

Part of #4831.

RFC: https://github.com/Azure/azure-rest-api-specs/blob/rfc/unified-examples-format/documentation/rfc/unified-examples-format.md

Build **`examples-resolve`**: given a target API version, resolve the applicable example for each operation.

### Scope
- Apply `since`: within a lineage pick the entry with the greatest `since` that is `<=` the target version.
- Use the **single linear version order from `service.yaml`** (see service.yaml epic #4825); no preview/stable special-casing.
- Substitute the `{api-version}` placeholder with the target version on materialization.

Depends on #4832 and on `service.yaml` version ordering (#4826).

Start by reading the unified examples RFC and the service.yaml version-ordering work, then review the prerequisite in #4832. The tool should accept a target API version, choose the applicable example per operation using the greatest eligible since value and the single service.yaml order, and materialize {api-version} with the target version.

Written by the indexing model from the issue text.