Turbopack: split up server actions modules for better treeshaking (#76877)
Closes PACK-4074
We really need to look into getting e2e tests for correct sourcemaps: PACK-4142
Fix Turbopack server action tree shaking by explicitly splitting up that module
```js
/* __next_internal_action_entry_do_not_use__ {"00c18c215a6b7cdc64bf709f3a714ffdef1bf9651d":"default","70e10665baac148856374b2789aceb970f66fec33e":"myAction"} */ import { createServerReference, callServer, findSourceMapURL } from "private-next-rsc-action-client-wrapper";
export var foo = /*#__PURE__*/ createServerReference("70e10665baac148856374b2789aceb970f66fec33e", callServer, void 0, findSourceMapURL, "myAction");
export var bar = /*#__PURE__*/ createServerReference("00c18c215a6b7cdc64bf709f3a714ffdef1bf9651d", callServer, void 0, findSourceMapURL, "default");
```
->
```js
"use turbopack no side effects";
export { foo } from "data:text/javascript,%2F%2A%20__next_internal_action_entry_do_not_use__%20%7B%2200ab21efdafbe611287bc25c0462b1e0510d13e48b%22%3A%22foo%22%7D%20%2A%2F%22use%20turbopack%20no%20side%20effects%22%3Bimport%7BcreateServerReference%2CcallServer%2CfindSourceMapURL%7Dfrom%22private-next-rsc-action-client-wrapper%22%3Bexport%20var%20foo%3D%2F%2A%23__PURE__%2A%2FcreateServerReference%28%2200ab21efdafbe611287bc25c0462b1e0510d13e48b%22%2CcallServer%2Cvoid%200%2CfindSourceMapURL%2C%22foo%22%29%3B";
export { bar } from "data:text/javascript,%2F%2A%20__next_internal_action_entry_do_not_use__%20%7B%2200ac840dcaf5e8197cb02b7f3a43c119b7a770b272%22%3A%22bar%22%7D%20%2A%2F%22use%20turbopack%20no%20side%20effects%22%3Bimport%7BcreateServerReference%2CcallServer%2CfindSourceMapURL%7Dfrom%22private-next-rsc-action-client-wrapper%22%3Bexport%20var%20bar%3D%2F%2A%23__PURE__%2A%2FcreateServerReference%28%2200ac840dcaf5e8197cb02b7f3a43c119b7a770b272%22%2CcallServer%2Cvoid%200%2CfindSourceMapURL%2C%22bar%22%29%3B";
````
- [x] Keep [sourcemaps](https://github.com/vercel/next.js/blob/canary/test/development/app-dir/source-mapping/README.md#server-actions)