FunctionDirective is not supported in `<script setup>` of Vue 2.7

### Version
2.7.8

### Reproduction link
[github.com](https://github.com/sxzz/vue2-directive-issue)







### Steps to reproduce
- `pnpm i`
- `pnpm run dev`

### What is expected?

No error

### What is actually happening?

Emit an error

` Error in directive color bind hook: "TypeError: Bind must be called on a function"`