runtime: implement SetFinalizer to fix syscall/js finalizeRef leak

src/runtime/gc_finalizer_sched_none.go

@@ -0,0 +1,6 @@
+//go:build (gc.conservative || gc.precise) && scheduler.none
+
+package runtime
+
+// scheduler.none has no goroutines; finalizers drain inline in wakeFinalizer.
+func spawnFinalizerRunner() {}