Add new telecom metrics for emergency dialer

These includes,
1. The source where user initiated the call.
2. The duration between START_CONNECTION and REQUEST_DISCONNECT.

Bug: 111818008
Test: manual and check the result of
'adb shell dumpsys telecom' for metrics data
Change-Id: I7d57ac29ad4bb6c8506b7a37b2f1bc63253fa9cb