Fix bug that dialpad fab wifi calling icon not showing.

Repro steps:
1. open dialer, click on FAB to open dialpad
2. make outgoing call, end call, press home
3. enable WiFi call
4. open dialer again, click on FAB to open dialpad

This is caused by change icon called after the FAB is visible and scaleIn won't do anything since it's already visible. But for some reason the icon is changed so nothing is drawn on the screen when the dialpad slide up. (dialpadfragment is visible even before it's slide up before user trigger it)
The fix is to scaleOut the FAB when the fragment onStop thus the changed icon will be correctly drawn.

Bug: 74586190
Test: manual
PiperOrigin-RevId: 189629441
Change-Id: I3dcbedcd171c992e5df14bff35758fce1bb67bc1