refactor(reactivity): adjust APIs

BREAKING CHANGE: Reactivity APIs adjustments:

- `readonly` is now non-tracking if called on plain objects.
  `lock` and `unlock` have been removed. A `readonly` proxy can no
  longer be directly mutated. However, it can still wrap an already
  reactive object and track changes to the source reactive object.

- `isReactive` now only returns true for proxies created by `reactive`,
   or a `readonly` proxy that wraps a `reactive` proxy.

- A new utility `isProxy` is introduced, which returns true for both
  reactive or readonly proxies.

- `markNonReactive` has been renamed to `markRaw`.

packages/reactivity/__tests__/reactive.spec.ts

@@ -3,7 +3,7 @@ import {
   reactive,
   isReactive,
   toRaw,
-  markNonReactive,
+  markRaw,
   shallowReactive
 } from '../src/reactive'
 import { mockWarn } from '@vue/shared'
@@ -146,10 +146,10 @@ describe('reactivity/reactive', () => {
     expect(reactive(d)).toBe(d)
   })
 
-  test('markNonReactive', () => {
+  test('markRaw', () => {
     const obj = reactive({
       foo: { a: 1 },
-      bar: markNonReactive({ b: 2 })
+      bar: markRaw({ b: 2 })
     })
     expect(isReactive(obj.foo)).toBe(true)
     expect(isReactive(obj.bar)).toBe(false)