types: improve readability of built-in type

packages/reactivity/src/reactive.ts

@@ -141,7 +141,7 @@ export function shallowReactive<T extends object>(
 }
 
 type Primitive = string | number | boolean | bigint | symbol | undefined | null
-type Builtin = Primitive | Function | Date | Error | RegExp
+export type Builtin = Primitive | Function | Date | Error | RegExp
 export type DeepReadonly<T> = T extends Builtin
  ? T
  : T extends Map<infer K, infer V>

packages/reactivity/src/ref.ts

@@ -16,7 +16,7 @@ import {
  isReadonly,
  isShallow
 } from './reactive'
-import type { ShallowReactiveMarker } from './reactive'
+import type { Builtin, ShallowReactiveMarker } from './reactive'
 import { createDep, Dep } from './dep'
 
 declare const RefSymbol: unique symbol
@@ -452,11 +452,6 @@ function propertyToRef(
  : (new ObjectRefImpl(source, key, defaultValue) as any)
 }
 
-// corner case when use narrows type
-// Ex. type RelativePath = string & { __brand: unknown }
-// RelativePath extends object -> true
-type BaseTypes = string | number | boolean
-
 /**
  * This is a special exported interface for other packages to declare
  * additional types that should bail out for ref unwrapping. For example
@@ -489,8 +484,7 @@ export type UnwrapRef<T> = T extends ShallowRef<infer V>
  : UnwrapRefSimple<T>
 
 export type UnwrapRefSimple<T> = T extends
- | Function
- | BaseTypes
+ | Builtin
  | Ref
  | RefUnwrapBailTypes[keyof RefUnwrapBailTypes]
  | { [RawSymbol]?: true }