Refactor AutomaticDataSwitchingPreference

Split into AutomaticDataSwitchingPreference.kt, and use
isMobileDataPolicyEnabledFlow.

Bug: 329061940
Test: manual - Set Automatic data switching
Test: unit test
Change-Id: I878ed70328307c0a5dba6dfb461ff5a85efbcf88
6 files changed