[Fix KernelKeyParser] Unify the logic of `operator()` in `KernelKeyParser` (#46560)

* add datatype check for ParseKernelKeyByInputArgs

* polish error message

* Actually, einsum has vector<Tensor> inpute with DataType::COMPLEX64, see test_einsum_v2.py

* headerfile remove enforce.h

paddle/phi/api/lib/kernel_dispatch.h

@@ -117,12 +117,10 @@ struct KernelKeyParser : ArgsIterator<KernelKeyParser> {
   }
 
   void operator()(const std::vector<Tensor>& x) {
+    if (!x.empty()) {
       const phi::TensorBase& tensor = *x.at(0).impl();
-    key_set.backend_set =
-        key_set.backend_set | detail::GetTensorBackendSet(tensor);
-    // TODO(chenweihang): select multi layout and dtype
-    key_set.layout = tensor.layout();
-    key_set.dtype = tensor.dtype();
+      AssignKernelKeySet(tensor);
+    }
   }
 
   void operator()(const paddle::optional<Tensor>& x) {