Fix(typedRoutes): fixed 'next' imports on TS < 5.0 (#46507)

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This is yet another follow-up PR of #46378...
In my discussion with the author of PR 46457, I figured out that
exporting with the .d.ts extension doesn't work in TS < 5.0, which I
didn't really notice because my projects were already using TS 5.0 and
Next's tests were passing. This PR just deletes the extension from the
export path.


## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the
feature request has been accepted for implementation before opening a
PR.
- [ ] Related issues linked using `fixes #number`
- [ ]
[e2e](https://github.com/vercel/next.js/blob/canary/contributing/core/testing.md#writing-tests-for-nextjs)
tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm build && pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

packages/next/src/build/webpack/plugins/next-types-plugin.ts

@@ -141,8 +141,8 @@ function createRouteDefinitions() {
   })
 
   return `declare module 'next' {
-  export { default } from 'next/types/index.d.ts'
-  export * from 'next/types/index.d.ts'
+  export { default } from 'next/types'
+  export * from 'next/types'
   
   type SearchOrHash = \`?\${string}\` | \`#\${string}\`