Implementation of "Enable 2G" for Settings.

(1) Adds KEY_HIDE_ENABLE_2G_BOOL to CarrierConfigManager, and
(2) Adds new reason ALLOWED_NETWORK_TYPES_REASON_ENABLE_2G.

Test: manual & atest -c Enable2gPreferenceControllerTest
Bug: b/163168917
Change-Id: I81052549f8dde491697c35365320145fd24c3842
Merged-In: I81052549f8dde491697c35365320145fd24c3842
5 files changed