fix(reactivity): track reactive keys in raw collection types

Also warn against presence of both raw and reactive versions of the
same object in a collection as keys.

fix #919

packages/reactivity/__tests__/collections/Set.spec.ts

@@ -1,7 +1,10 @@
 import { reactive, effect, isReactive, toRaw } from '../../src'
+import { mockWarn } from '@vue/shared'
 
 describe('reactivity/collections', () => {
   describe('Set', () => {
+    mockWarn()
+
     it('instanceof', () => {
       const original = new Set()
       const observed = reactive(original)
@@ -380,5 +383,34 @@ describe('reactivity/collections', () => {
       expect(set.delete(entry)).toBe(true)
       expect(set.has(entry)).toBe(false)
     })
+
+    it('should track deletion of reactive entries in raw set', () => {
+      const raw = new Set()
+      const entry = reactive({})
+      raw.add(entry)
+      const set = reactive(raw)
+
+      let dummy
+      effect(() => {
+        dummy = set.has(entry)
+      })
+      expect(dummy).toBe(true)
+
+      set.delete(entry)
+      expect(dummy).toBe(false)
+    })
+
+    it('should warn when set contains both raw and reactive versions of the same object', () => {
+      const raw = new Set()
+      const rawKey = {}
+      const key = reactive(rawKey)
+      raw.add(rawKey)
+      raw.add(key)
+      const set = reactive(raw)
+      set.delete(key)
+      expect(
+        `Reactive Set contains both the raw and reactive`
+      ).toHaveBeenWarned()
+    })
   })
 })