Save the last KEY_EMERGENCY_CALLBACK_MODE_SUPPORTED_BOOL

Operators, supporting emergency callback mode, request
to enter emergency callback mode when there is no SIM.
KEY_EMERGENCY_CALLBACK_MODE_SUPPORTED_BOOL is valid only
when there is a valid SIM.
To comply with the requirement, EmergencyStateTracker
shall save the last configuration for the last valid subscription
and shall refer to the saved configuration when the SIM is removed.

Bug: 288825086
Test: atest EmergencyStateTrackerTest
Change-Id: I751b7dc4d08f3bf96d52175eaa2d4a990d7d1631