update registering_seconds and unregistered_seconds for IMS-capable RATs

- only count IMS-capable RATs

Bug: 284220679
Bug: 265993889
Test: atest ImsStatsTest
Test: atest com.android.internal.telephony.metrics
Test: manual test to check ims registering and unregistered duration
while turning wifi on and off

Change-Id: Icb058ff8bcfa0eedaf64870e70a9d7a508f8fe9b