Make StatusBarSignalPolicy startable

Bug: 264539100
Test: Made sure the airplane icon is updated in the status bar
when it is toggled from the QS Tile and the settings app.
This was done on a Pixel tablet.
Flag: com.android.systemui.status_bar_signal_policy_refactor

Change-Id: I7b479132e11bd811e7f9b47af0b42d67ec0d8b24