The loadLibrary() function returns a Future<void>
that completes successfully when the code in the library
is available for use and completes with an error otherwise.
All usage of symbols from the deferred library should be
guarded behind a completed loadLibrary() call. All imports
of the library must be marked as deferred for it to be
compiled appropriately to be used in a deferred component.
If a component has already been loaded, additional calls
to loadLibrary() complete quickly (but not synchronously).
The loadLibrary() function can also be called early to
trigger a pre-load to help mask the loading time.

    You can find another example of deferred import loading in
Flutter Gallery’s lib/deferred_widget.dart.

Step 3: Building the app

Use the following flutter command to build a deferred
components app:

flutter build appbundle