Enable HearingAids#AudioRouting page search if the device supports hearing aid

Enable searching in the AccessibilityAudioRoutingFragment only if the
page is available and the device supports hearing aid.

Bug: 353853318
Test: atest AccessibiilityAudioRoutingFragmentTest
Test: Manually. Add screen recording of search results to the bug
Test: Manually set the support to hearing aids to false and verify that searches to the page contents are not available
Flag: com.android.settings.accessibility.fix_a11y_settings_search
Change-Id: I6786c51438d49ff9bb1d458d312ec09bd16098a4