Allows for system navigation settings to be added dynamically.

This allows for controller-backed preferences to be added or
overridden via xml.

Similarly, if the controllers cause all of the preferences for
2 or 3 button nav to be unavailable, we hide the settings button.

Bug: 324036308
Test: Manual and unit tests
Flag: NA
Change-Id: I2371f3173076172489966728ac69c8767570cd56