Assume video calls supported until user chooses phone account.

When an outgoing Call has no target phone account, initially assume video
calling is supported by the call.  Once a target phone account is set,
ensure the video state of the outgoing call is updated based on whether
video calling is supported by the target phone account.

Bug: 31094340
Change-Id: Iee1bc542b63d9be6d2f76206fdc9b87674db271c