As raised here, Android Studio throws the following error for the newly added GutenbergDialogFragment class:
Cannot access 'androidx.activity.result.ActivityResultCaller' which is a supertype of 'org.wordpress.android.editor.gutenberg.GutenbergDialogFragment'. Check your module classpath for missing or conflicting dependencies
The error is visible when running the app in the latest version of Android Studio (4.2.1):

Logging this issue as, although the error doesn't block the code from working, it does indicate that there may be a misalignment in dependency versions in the editor package's build.gradle.