Of the original 4 examples, the first 3 mostly covered the same API features and occupied quite a bit of real-estate at the top of https://api.flutter.dev/flutter/material/FloatingActionButton-class.html.  Additionally the illustrations and the code samples didn't match in some cases.

Replaced examples 0,1,2 with one example that changes attributes of the FAB when it's pushed. 

Fixes https://github.com/flutter/flutter/issues/128048