fix: ensure render watcher of manually created instance is correctly tracked in owner scope

fix #12701

src/core/instance/lifecycle.ts

@@ -209,6 +209,7 @@ export function mountComponent(
   // we set this to vm._watcher inside the watcher's constructor
   // since the watcher's initial patch may call $forceUpdate (e.g. inside child
   // component's mounted hook), which relies on vm._watcher being already defined
+  vm._scope.on()
   new Watcher(
     vm,
     updateComponent,
@@ -216,6 +217,7 @@ export function mountComponent(
     watcherOptions,
     true /* isRenderWatcher */
   )
+  vm._scope.off()
   hydrating = false
 
   // flush buffer for flush: "pre" watchers queued in setup()

src/core/observer/watcher.ts

@@ -72,10 +72,8 @@ export default class Watcher implements DepTarget {
     isRenderWatcher?: boolean
   ) {
     recordEffectScope(this, activeEffectScope || (vm ? vm._scope : undefined))
-    if ((this.vm = vm)) {
-      if (isRenderWatcher) {
-        vm._watcher = this
-      }
+    if ((this.vm = vm) && isRenderWatcher) {
+      vm._watcher = this
     }
     // options
     if (options) {