e911 call should go on same SIM as ongoing VoLTE call.

- In DSDA devices, e911 call should go on the same PhoneAccountHandle
  of ongoing call, as long as ongoing call is on Wifi or cellular.
- If the ongoing call is over cross-SIM calling, e911 call will be made
  in the other Phone object at TelephonyConnectionService#getPhoneForAccount().

Test: Manual testing:
confirm e911 call goes on same sub as existing VoLTE/WiFi call .
confirm e911 call goes on different sub as existing cross-SIM call.

New UTs in CallsManagerTest

Bug: 274537723
Change-Id: I40cc213d050c74ad88054b37a8a844ab3bbf948e