The package must have at least one '.' separator

Currently the plugin disallows creating an app with Android package name like "myorg.myproject"

## Steps to Reproduce

- Open Android Studio with Flutter plugin installed
- Click "New Flutter Project"
- Input project name and organization of one word each, e.g "myproject" and "myorg"
- An error will occur: _The package must have at least one '.' separator_

However:
- Android [allows](https://developer.android.com/studio/build/configure-app-module#set-application-id) it: _must have at least two segments (one or more dots)_
- Native Android project in Android Studio can be created with such name
- Flutter command-line tool also allows it: `flutter create myproject --org myorg`

## Version info

Flutter 2.10.5 • channel stable • https://github.com/flutter/flutter.git
Framework • revision 5464c5bac7
Engine • revision 57d3bac3dd
Tools • Dart 2.16.2 • DevTools 2.9.2

Android Studio Bumblebee | 2021.1.1 Patch 3
Flutter plugin 67.1.1
Dart plugin 211.7817