Auxiliary tooling: examples-scaffold + examples-diff

[timotheeguerin]

Part of #4831.

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

Auxiliary example tooling.

Scope

• examples-scaffold — generate faked initial examples from the API surface, replacing OAV's faked-example generation.
• examples-diff — show what changed in an example between versions.

Depends on #4832 (schema).