Fixes #86590

When desktop support is not present in an existing project, certain
flutter tool commands raise an error that direct the user to
documentation on how to add desktop support to an existing Flutter
project. In a recent revamp of the webside, the URL was very slightly
changed (flutter.dev -> docs.flutter.dev).

This updates the error message to output the new URL.

Issue: https://github.com/flutter/flutter/issues/94398

* Add a new PrebuiltFlutterApplicationPackage interface.

* Review feedback

* Rename bundleDir to uncompressedBundle

This reverts commit 00658736.

This reverts commit cb378edc.