Migrate LTE_CA flag to NRI from DSRI

Migrate the isUsingCarrierAggregation flag from
DataSpecificRegistrationInfo to NetworkRegistrationInfo.

This does a few things:
-Allows LTE_CA to be properly reported even in IWLAN legacy
 mode.
-Removes one additional layer of drilling up/down to store
 and retrieve the boolean flag.
-Simplifies the ratcheting logic.

Bug: 156676862
Test: atest FrameworksTelephonyTests
Change-Id: Ia7d9344e590efe0dcf2c7ba6d44d925f72d1e626