Previously we hide the preference when Bluetooth is off since it's only used for showing connected hearing aids and acting as a shortcut to device detail page.
However, the preference is now a new page of multiple controls, we probably shouldn't hide the preference the Bluetooth is off. Those controls should be accessible even if the Bluetooth is off.
Bug: 284092084
Test: make RunSettingsRoboTests ROBOTEST_FILTER=HearingAidHelperTest
Change-Id: I647a187d73bd673c8ac8ab366579ba92c22ce1dc
* Extract the common part into HearingAidHelper.
* Remove abstract getHearingDevice(). Change to get the hearing device when needed.
* Move several classes from Bluetooth into Accessibility
Bug: 281783079
Test: make RunSettingsRoboTests ROBOTEST_FILTER="(HearingDeviceAudioRoutingBasePreferenceControllerTest|AccessibilityHearingAidPreferenceControllerTest|HearingAidHelperTest|HearingAidAudioRoutingPreferenceControllerTest|HearingDeviceCallRoutingPreferenceControllerTest)"
Change-Id: I79049107409b7086c6dcc8d48a6323e171ed1535
