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__/effect.spec.ts

@@ -6,7 +6,7 @@ import {
   TrackOpTypes,
   TriggerOpTypes,
   DebuggerEvent,
-  markNonReactive,
+  markRaw,
   ref
 } from '../src/index'
 import { ITERATE_KEY } from '../src/effect'
@@ -732,9 +732,9 @@ describe('reactivity/effect', () => {
     expect(dummy).toBe(3)
   })
 
-  it('markNonReactive', () => {
+  it('markRaw', () => {
     const obj = reactive({
-      foo: markNonReactive({
+      foo: markRaw({
         prop: 0
       })
     })