DSDA: Hold active call when placing 2nd call

- When "Add call" is placed from Dialer to choose another sub for a 2nd call,
 the active call on the existing sub is placed on hold.
- The dial out to the modem is sequenced after the HOLD completes.

Bug:269365977
Test: Live test for Adding 2nd call from other sub in cross-SIM calling.
TelephonyConnectionServiceTest#testHoldOnOtherSubForVirtualDsdaDevice

Change-Id: I8af69bccedbaf422f08f36e21d9f4056b83517ff
2 files changed