rename optimize_graph to graph_optimize (#16082)

ggml/src/ggml-webgpu/ggml-webgpu.cpp

@@ -823,7 +823,7 @@ static ggml_backend_i ggml_backend_webgpu_i = {
     /* .graph_compute           = */ ggml_backend_webgpu_graph_compute,
     /* .event_record            = */ NULL,
     /* .event_wait              = */ NULL,
-    /* .optimize_graph          = */ NULL,
+    /* .graph_optimize          = */ NULL,
 };
 
 /* End GGML Backend Interface */