Fix compilation of exported server functions (#86296)
With this PR we are restructuring how the Next.js compiler transforms server function modules (`'use server'` or `'use cache'` directive at the top of the file).
The workaround for skipping the registration of exported `'use cache'` functions is removed. All exported server functions are now properly registered during visitor traversal, which fixes incorrect server reference information bytes in server reference IDs in some circumstances (see #86292 for example).
We're also adding support for string literal exports, e.g.:
```js
'use server'
async function foo() {}
export { foo as '📙' }
```
