x-id emission: typespec-autorest + transitional JSON

Part of the Unified Examples Format epic.

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

Add **`x-id` emission** to `@azure-tools/typespec-autorest`.

### Scope
- Emit an **`x-id`** extension (the full operation identity, `$namespace` + operation key) on every operation.
- **Stop embedding** `x-ms-examples` `$ref` blocks in generated Swagger.
- Transitional: optionally emit `x-ms-examples` JSON generated from the new format for consumers not yet migrated.
- Confirm the **doc-team pipeline** can consume `x-id` in place of the embedded `$ref`.

Read documentation/rfc/unified-examples-format.md first, then trace x-id and x-ms-examples generation in @azure-tools/typespec-autorest and check the doc-team pipeline entry point. Done means every operation emits its full x-id, embedded x-ms-examples $ref blocks are removed, transitional JSON output is optional, and the pipeline consumes x-id.

Written by the indexing model from the issue text.