Move a11y indexing from DynamicContentMonitor to loader

This is necessary to kill DynamicContentMonitor later

- Removed all logic related to indexing accesiblitysetting from the
  monitor class and AccessibilitySetting page itself
- Created a loader to search against A11yServices at runtime

I noticed adding a loader in SearchResultsAdapter is rather manual. It's
something we should consider refactor in the future.

Bug: 64310452
Test: robotests
Change-Id: Iff31aff65ce000991229433f294e2ec69af99da2

src/com/android/settings/search/SearchFeatureProviderImpl.java

@@ -54,6 +54,13 @@ public class SearchFeatureProviderImpl implements SearchFeatureProvider {
                 cleanQuery(query), getSiteMapManager());
     }
 
+    @Override
+    public AccessibilityServiceResultLoader getAccessibilityServiceResultLoader(Context context,
+            String query) {
+        return new AccessibilityServiceResultLoader(context, cleanQuery(query),
+                getSiteMapManager());
+    }
+
     @Override
     public SavedQueryLoader getSavedQueryLoader(Context context) {
         return new SavedQueryLoader(context);