Remove unnecessary ALS re-exports from `entry-base.ts` (#91527)
The `workAsyncStorage`, `workUnitAsyncStorage`, and `actionAsyncStorage`
instances were re-exported from `entry-base.ts` so that they could be
accessed as properties of the bundled page module (`ComponentMod`). This
indirection is no longer necessary because the `.external.ts` naming
convention forces webpack to externalize these modules to `commonjs
next/dist/...` (via `resolveNextExternal` in `handle-externals.ts`), and
the `turbopack-transition: 'next-shared'` import attributes achieve the
same for Turbopack. Both mechanisms guarantee that the bundled page
module and direct imports resolve to the same singleton instance.
This removes the three re-exports from `entry-base.ts` and replaces all
`ComponentMod`-based access with direct imports from the `.external`
modules in `static-paths/app.ts` and `action-handler.ts`.
