examples-resolve tool

[timotheeguerin]

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 Epic: service.yaml rollout #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).