Instantiate pref controllers from xml if it's defined.

- If a <preference> tag also defines a controller, we will try to
  instantiate it before displaying the UI. The same logic is shared by
  BaseSearchIndexProvider so it also drives search suppression.

- If user also defines a list of controllers programatically, the
  programatically created ones takes precedence.

Bug: 73668763
Test: WIP
Change-Id: I7aecec270bcd3af261e012ef1f6995d2a523cfa1

tests/robotests/assets/grandfather_not_in_search_index_provider_registry

@@ -1,2 +1 @@
 com.android.settings.display.ScreenZoomPreferenceFragmentForSetupWizard
-com.android.settings.search.indexing.FakeSettingsFragment

tests/robotests/assets/grandfather_not_sharing_pref_controllers_with_search_provider

@@ -1 +1,5 @@
-com.android.settings.fuelgauge.PowerUsageSummary
+com.android.settings.datausage.DataUsageSummaryLegacy
+com.android.settings.fuelgauge.PowerUsageSummary
+com.android.settings.fuelgauge.PowerUsageAdvanced
+com.android.settings.search.indexing.FakeSettingsFragment
+com.android.settings.system.SystemDashboardFragment