Introduce new resource overlay for Virtual DSDA

- "Virtual DSDA" functionality is planned for P22+ on Android U.
- New flag "virtual_dsda_enabled" denotes support for in-call IMS connectivity
 on both subs with just single active logical modem / data line.

Bug: 249857869
Test: Live test for incoming call reception on 2nd sub. New UTs:
TelephonyConnectionServiceTest#testSecondCallDifferentSubWontDisconnectForDsdaDevice()
TelephonyConnectionServiceTest#testDontDisconnectDifferentSubForDsdaDevice()

Change-Id: I42dc44afe17546deabdae303c4a48892dc5d5e8c