fix(reactivity): should not trigger map keys iteration when keys did not change

fix #877

packages/reactivity/src/collectionHandlers.ts

@@ -1,5 +1,5 @@
 import { toRaw, reactive, readonly } from './reactive'
-import { track, trigger, ITERATE_KEY } from './effect'
+import { track, trigger, ITERATE_KEY, MAP_KEY_ITERATE_KEY } from './effect'
 import { TrackOpTypes, TriggerOpTypes } from './operations'
 import { LOCKED } from './lock'
 import { isObject, capitalize, hasOwn, hasChanged } from '@vue/shared'
@@ -134,12 +134,16 @@ function createForEach(isReadonly: boolean) {
 function createIterableMethod(method: string | symbol, isReadonly: boolean) {
   return function(this: IterableCollections, ...args: unknown[]) {
     const target = toRaw(this)
-    const isPair =
-      method === 'entries' ||
-      (method === Symbol.iterator && target instanceof Map)
+    const isMap = target instanceof Map
+    const isPair = method === 'entries' || (method === Symbol.iterator && isMap)
+    const isKeyOnly = method === 'keys' && isMap
     const innerIterator = getProto(target)[method].apply(target, args)
     const wrap = isReadonly ? toReadonly : toReactive
-    track(target, TrackOpTypes.ITERATE, ITERATE_KEY)
+    track(
+      target,
+      TrackOpTypes.ITERATE,
+      isKeyOnly ? MAP_KEY_ITERATE_KEY : ITERATE_KEY
+    )
     // return a wrapped iterator which returns observed versions of the
     // values emitted from the real iterator
     return {