feat(types): expose DeepReadonly type (#1606)

Author: Pick

packages/reactivity/src/index.ts

@@ -22,7 +22,8 @@ export {
   shallowReadonly,
   markRaw,
   toRaw,
-  ReactiveFlags
+  ReactiveFlags,
+  DeepReadonly
 } from './reactive'
 export {
   computed,

packages/reactivity/src/reactive.ts

@@ -74,7 +74,7 @@ export function shallowReactive<T extends object>(target: T): T {
 
 type Primitive = string | number | boolean | bigint | symbol | undefined | null
 type Builtin = Primitive | Function | Date | Error | RegExp
-type DeepReadonly<T> = T extends Builtin
+export type DeepReadonly<T> = T extends Builtin
   ? T
   : T extends Map<infer K, infer V>
     ? ReadonlyMap<DeepReadonly<K>, DeepReadonly<V>>