TCGC + consumers adoption of `examples.yaml`

Part of #4831.

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

Adopt the new examples format in the **consumers**.

### Scope
- **TCGC** parses `examples.yaml` and surfaces real example content (all language generators consume examples via TCGC, so TCGC must adopt the format).
- **SDK test generation** consumes resolved examples (via `examples-resolve`) to generate test cases.
- Join Swagger operations to examples via **`x-id`** rather than embedded `$ref`.

Depends on #4834 (resolve) and #4835 (`x-id` emission).