Split Ambient Display settings.

1. Reverting the changes for Display->Ambient Display; this setting
   will control incoming notification pulse.
2. Added 2 separate entries in gestures settings to control pick up
   and double tap gestures-triggered pulsing for Ambient Display.
3. Added automated tests to verify the preference initializes to the
   correct default value, and also verify that toggling the preference
   updates the corresponding settings correctly.

Test: make SettingsTests

Bug: 30595437
Change-Id: I125bf75fc4ccfea126a00ffae4207fcb789f487a