[V1][Platform] Add supports_structured_output() method to Platform (#475)

### What this PR does / why we need it?
Add `supports_structured_output()` method to Platform, find more details
at https://github.com/vllm-project/vllm/pull/16148.

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

vllm_ascend/platform.py

@@ -164,3 +164,7 @@ class NPUPlatform(Platform):
         model configuration.
         """
         return True
+
+    @classmethod
+    def supports_structured_output(cls) -> bool:
+        return True