Add ActivityIndicator to MaterialFloatingButton and MaterialIconButton

[AgustinBonilla]

We have to add the possibility to show that these buttons are busy like we are doing with the MaterialButton.

Also, we will remove the workaround that we have implemented in the MaterialTopAppBar to show activity indicators.

Desirable properties (they are in the MaterialButton):

• IsBusy
• BusyColor
• CustomActivityIndicator
• ActivityIndicatorSize