[V1][Structured Output] Add supports_structured_output() method to Platform (#16148)

Signed-off-by: shen-shanshan <467638484@qq.com>

vllm/platforms/xpu.py

@@ -140,3 +140,7 @@ class XPUPlatform(Platform):
     @classmethod
     def get_device_communicator_cls(cls) -> str:
         return "vllm.distributed.device_communicators.xpu_communicator.XpuCommunicator"  # noqa
+
+    @classmethod
+    def supports_structured_output(cls) -> bool:
+        return True