Add toggle to allow or disable null algorithms

This adds the allow null algorithms toogle to the Settings UI.

If supported by the smartphone baseband, the toggle allows users to opt
out of null algorithms, unencrypted cellular communication, for all
cellular generations.

This toggle is behind a feature flag that is off by default. It also
requires radio network HAL 2.1 or later to show.

Co-authored-by: Gil Cukierman <cukie@google.com>
Bug: b/237529943
Test: atest NullAlgorithmsPreferenceControllerTest
Test: adb shell device_config put cellular_security
enable_null_cipher_toggle true; // On cuttlefish, you can now see the
toggle in SIM settings.

Change-Id: Ia03cceee5463171ca455fa0624b911e06f222d2d