ServiceStateStats tracks cross-SIM calling reg

- New boolean field 'is_iwlan_cross_sim' that can be read for
multi-SIM devices where the voiceRat is NETWORK_TYPE_IWLAN.

Bug: 294240210
Test: Updated ServiceStateStatsTest, on-device testing with go/telephony-ww-local-testing
Change-Id: I0ad59331ae18b39c762d57fc90bd3fd8248f3ef1