Handle Device Admin Updates to 2G per Phone Instance

Problem:
A previous implementation (aosp/2371949) honoring the no_cellular_2g restriction
operated at the subscription level and was complex and prone to race
conditions between subscription loading and carrier configs. This
manifested in devices booting without applying the admin policy
sometimes.

Solution:
Move the enforcement of the admin policy into each instance
of Phone. Before allowed network types are sent to the modem, a
check against the admin policy is performed. If the no_cellular_2g
restriction is set, 2g is disabled in the effective bitmap that is
passed to the modem. Note that Phone.sendSubscriptionSetting is called
by ServiceStateTracker when a new subscription is added so this change
is piggy backing off of that call to ensure the admin policy gets
enforced on every call.

Introduce BroadcastReceiver, TelephonyAdminReceiver, that calls
Phone.sendSubscriptionSettings when the relevant 2g admin policy
changes.

Bug: 266472206
Test: atest TelephonyAdminReceiver
Test: atest GsmCdmaPhoneTest
Test: Manual testing on cuttlefish with the TestDPC app. Asserted that
the 2g admin policy is applied on boot and persisted across reboots.

Change-Id: Iaf15dca36c4a1b383d75b65d157578fdeb4ad989