types: add refInFor to VNodeData (#8229)

types/test/options-test.ts

@@ -176,7 +176,8 @@ Vue.component('component', {
         fontSize: '14px'
       },
       key: 'myKey',
-      ref: 'myRef'
+      ref: 'myRef',
+      refInFor: true
     }, [
       createElement(),
       createElement("div", "message"),

types/vnode.d.ts

@@ -36,6 +36,7 @@ export interface VNodeData {
   slot?: string;
   scopedSlots?: { [key: string]: ScopedSlot };
   ref?: string;
+  refInFor?: boolean;
   tag?: string;
   staticClass?: string;
   class?: any;