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: 112168722
Bug: 111818008

Test: manual and check the result of
'adb shell dumpsys telecom' for metrics data
Change-Id: Iddc7f256362abe9fe252bd12cead05a7d77d329e
Merged-In: Iddc7f256362abe9fe252bd12cead05a7d77d329e