Fix animation of first time showing dialpad FAB.

In order to correctly show animation, we have to ensure:
1. fab.scaleIn() is not called before dialpad is slide up.
2. fab is invisible before scaleIn is called.

Caveat:
This change is not tested on old UI (DialtactsActivity) since it's deprecated.
Test: manual
PiperOrigin-RevId: 189765153
Change-Id: Iada96b2789f96ca1612ae2048020a649f8b57b6b