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/src/reactive.ts

@@ -20,7 +20,7 @@ const readonlyToRaw = new WeakMap<any, any>()
 
 // WeakSets for values that are marked readonly or non-reactive during
 // observable creation.
-const nonReactiveValues = new WeakSet<any>()
+const rawValues = new WeakSet<any>()
 
 const collectionTypes = new Set<Function>([Set, Map, WeakMap, WeakSet])
 const isObservableType = /*#__PURE__*/ makeMap(
@@ -32,7 +32,7 @@ const canObserve = (value: any): boolean => {
     !value._isVue &&
     !value._isVNode &&
     isObservableType(toRawType(value)) &&
-    !nonReactiveValues.has(value) &&
+    !rawValues.has(value) &&
     !Object.isFrozen(value)
   )
 }
@@ -132,19 +132,24 @@ function createReactiveObject(
 }
 
 export function isReactive(value: unknown): boolean {
-  return reactiveToRaw.has(value) || readonlyToRaw.has(value)
+  value = readonlyToRaw.get(value) || value
+  return reactiveToRaw.has(value)
 }
 
 export function isReadonly(value: unknown): boolean {
   return readonlyToRaw.has(value)
 }
 
+export function isProxy(value: unknown): boolean {
+  return readonlyToRaw.has(value) || reactiveToRaw.has(value)
+}
+
 export function toRaw<T>(observed: T): T {
   observed = readonlyToRaw.get(observed) || observed
   return reactiveToRaw.get(observed) || observed
 }
 
-export function markNonReactive<T extends object>(value: T): T {
-  nonReactiveValues.add(value)
+export function markRaw<T extends object>(value: T): T {
+  rawValues.add(value)
   return value
 }