Request: add sample for using ExtendedFloatingActionButton

[AndroidDeveloperLB]

This:

https://material.io/develop/android/components/extended-floating-action-button/

[ricknout]

I am doing the components in alphabetical order. I plan to do an article on FloatingActionButton & ExtendedFloatingActionButton soon :-)

[AndroidDeveloperLB]

I see. Thank you.