VoiceCallSessionStats captures Cross-SIM Calling

- Adds boolean fields for "is_iwlan_cross_sim_*" that shadow the
  "rat_at_start", "rat_at_end" and "rat_at_connected" fields and are
applicable when the NetworkType is IWLAN.
- Separate booleans are necessary since NetworkType does not have a
  dedicated field for cross-SIM calling.

Bug: 294240210
Test: Updated VoiceCallSessionStatsTest, on device testing with go/telephony-ww-local-testing
Change-Id: I2c94de91d8187d6c077c66f3a7c7c092c63a58f9