Add `__nextjs_pure` helper (#57286)
### What?
Safely drop `__nextjs_pure` from next internals in transform
```js
import {__nextjs_pure} from 'next/dist/build/swc/helpers'
__nextjs_pure(console.log("test!"))
```
becomes
```js
/*#__PURE__*/ console.log("test!");
```
so it will be dropped by the minifier - terser and swc minifier will
both work.
### Why?
Adding pure comments from JS world with swc transform is complex. This
would be a helper for the case if we want to create "pure" expressions.
### How?
Closes WEB-1829
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Co-authored-by: Jiachi Liu <inbox@huozhi.im>
