Add domain selection connection for SMS

This is for a normal and an emergency SMS domain selection connection.
Each domain selection connection acts as a client to communicate with
the domain selection service.

Bug: 243377249
Test: atest SmsDomainSelectionConnectionTest
Test: atest EmergencySmsDomainSelectionConnectionTest
Test: manual (verify IMS/GSM/CDMA MO SMS for normal/emergency SMS when domain selection disabled)
Test: manual (verify retry SMS for normal/emergency SMS when domain selection disabled)
Test: manual (verify IMS/GSM/CDMA MO SMS for normal/emergency SMS when domain selection enabled)
Test: manual (verify retry SMS for normal/emergency SMS when domain selection enabled)
Change-Id: I75682ecadefbfd5b75a4658123ebb6eab93df3d3