docs: Clarified purpose of application "name" attr within manifest.

Improved descriptions of the "name" attribute of the <application>
element, which appears within an Android app's <manifest> element in
its manifest file. Also clarified connection between this attribute
and custom subclasses of the Application class.

Bug: 1232595
Change-Id: I79b6bd31224c7669b5dc509914a01ead84a049dc
Abandoned-Change-Id: Icee66f6b8df55c7fad414b4c19939a483dc7a165