Add Content Sizing Sample

[mboetger]

This is a sample add-to-app Android project based off the existing add-to-app Android sample project. This one makes minor changes to show how content-sizing can be achieved.

Adding a content resizing sample for Android to support
flutter/flutter#179753

Pre-launch Checklist

• I read the [Flutter Style Guide] recently, and have followed its advice.
• I signed the [CLA].
• I read the [Contributors Guide].
• I have added sample code updates to the [changelog].
• I updated/added relevant documentation (doc comments with ///).