Combine data roaming from user action into one preference

Instead of using DATA_ROAMING_IS_USER_SETTING_KEY for SSSS and
DATA_ROAMING + subId for DSDS, combine both into
DATA_ROAMING_IS_USER_SETTING_KEY + subId.

Test: verify data roaming settings persisted across reboots
Test: verify data roaming settings persisted across upgrades
Test: verify data roaming settings correct based on carrier configs
Test: atest DataSettingsManagerTest
Bug: 259604889
Change-Id: Id73e66b2fd96a367ff469b464bf01bedddf6fdd3
Merged-In: Id73e66b2fd96a367ff469b464bf01bedddf6fdd3