Added toggling testing mode via secret code support

By dialing *#*#CMAS#*#* on the debug build, we can
toggle the cell broadcast testing mode. For example,
testing alert toggle is hidden for Japanese users, by
dialing this code, the toggle will show up for testers
to enable. In the future we will add hidden menu for
different carrier requirement (e.g. DBGF alert menu).

Test: Manual
Bug: 144230993
Change-Id: If4121d939457dfbb5907d1655b32153f3f6947fc
7 files changed