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/InstalledAppResultLoader.java

@@ -163,8 +163,9 @@ public class InstalledAppResultLoader extends AsyncLoader<Set<? extends SearchRe
      * appName: Abcde, query: bc, Returns NAME_NO_MATCH
      * appName: Abcde, query: xyz, Returns NAME_NO_MATCH
      * appName: Abc de, query: de, Returns 4
+     * TODO: Move this to a common util class.
      */
-    private int getWordDifference(String appName, String query) {
+    static int getWordDifference(String appName, String query) {
         if (TextUtils.isEmpty(appName) || TextUtils.isEmpty(query)) {
             return NAME_NO_MATCH;
         }