Show dialpad button for VT calls, cleanup dialpad on rotation.

1. Show the dialpad button for VT calls (this was easy).
2. In testing I realized there were some other dialpad scenarios that
did not work properly:
- The dialpad visibility state was not properly restored after rotation.
- The auto-fullscreen code could hide the call card when the dialpad was
showing, resulting in an inability to hide the dialpad.
- In landscape it was possible to tap between the call card and the
dialpad and cause the call card to be hidden.
- If user goes to background in fullscreen mode and then opens dialer and
chooses to show the dialpad, the app is still in fullscreen and it is not
possible to hide the dialpad.
3. Noticed an issue related to the fact mIsFullScreen in InCallPresenter
is static, and after rotation you're always defaulting to not fullscreen.
Fixed by clearing fullscreen state on rotation to match actuality.

Bug: 21296950
Change-Id: I2c7a666a50e2284b1d22db43c443b34109cff9b1