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