Fix next-types-plugin generated files for Node16/NodeNext (#47571)

### What / Why / How?

In a project with `"type": "module"` in `package.json` and a `compilerOptions.moduleResolution` of `Node16` or `NodeNext` in `tsconfig.json`, running `tsc` will yield errors like the following:

```
.next/types/app/[...not_found]/page.ts:1:40 - error TS2307: Cannot find module 'next/dist/lib/metadata/types/metadata-interface' or its corresponding type declarations.

1 import type { ResolvingMetadata } from 'next/dist/lib/metadata/types/metadata-interface';
                                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.next/types/app/layout.ts:2:24 - error TS2835: Relative import paths need explicit file extensions in EcmaScript imports when '--moduleResolution' is 'node16' or 'nodenext'. Did you mean '../../../app/layout.jsx'?

2 import * as entry from '../../../app/layout'
                         ~~~~~~~~~~~~~~~~~~~~~

.next/types/app/layout.ts:3:40 - error TS2307: Cannot find module 'next/dist/lib/metadata/types/metadata-interface' or its corresponding type declarations.

3 import type { ResolvingMetadata } from 'next/dist/lib/metadata/types/metadata-interface'
                                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

These files are checked because of the following `tsconfig.json` line which Next.js adds:

```diff
{
  "include": [
+    ".next/types/**/*.ts",
  ]
}
```

Adding the extensions will make it work with these projects and still maintain backwards compatibility with other TypeScript / module configurations.

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

@@ -44,11 +44,11 @@ function createTypeGuardFile(
   }
 ) {
   return `// File: ${fullPath}
-import * as entry from '${relativePath}'
+import * as entry from '${relativePath}.js'
 ${
   options.type === 'route'
-    ? `import type { NextRequest } from 'next/server'`
-    : `import type { ResolvingMetadata } from 'next/dist/lib/metadata/types/metadata-interface'`
+    ? `import type { NextRequest } from 'next/server.js'`
+    : `import type { ResolvingMetadata } from 'next/dist/lib/metadata/types/metadata-interface.js'`
 }
 
 type TEntry = typeof entry
@@ -637,10 +637,18 @@ export class NextTypesPlugin {
               })
             }
 
+            // Support tsconfig values for "moduleResolution": "Node16" or "NodeNext"
+            const packageJsonTypePath = path.join('types', 'package.json')
+            const packageJsonAssetPath =
+              assetDirRelative + '/' + normalizePathSep(packageJsonTypePath)
+            assets[packageJsonAssetPath] = new sources.RawSource(
+              '{"type": "module"}'
+            ) as unknown as webpack.sources.RawSource
+
             const linkTypePath = path.join('types', 'link.d.ts')
-            const assetPath =
+            const linkAssetPath =
               assetDirRelative + '/' + normalizePathSep(linkTypePath)
-            assets[assetPath] = new sources.RawSource(
+            assets[linkAssetPath] = new sources.RawSource(
               createRouteDefinitions()
             ) as unknown as webpack.sources.RawSource
           }