Change underlying preferenceControllers to an ArrayMap of Lists.

Previously, DashboardFragment stores preference controllers in an
ArrayMap of <Class, AbstractPreferenceController>. Thus when there are
multiple controllers of same class (ie. multiple
PreferenceCategoryControllers), they cannot be stored simultaneously.
This changes the value to a List so we can store multiple controllers of
the same Class without extraneous sub-classing.

Bug: 70949662
Test: All existing tests still pass.
Added
DashboardFragmentTest#testPreferenceControllerSetter_shouldAddAndNotReplace
and DashboardFragmentTest#updateState_doesNotSkipControllersOfSameClass.
Change-Id: I397e8c91977ea1180d48a3af75dd4058bf1175c0