Fixes fail test cases in AccessibilitySettingsTest

AccessibilityHearingAidPreferenceController can't be instantiated
correctly in tests with the lack of LocalBluetoothManager. This causes
null pointer exception when
AccessibilityHearingAidPreferenceController.setFragmentManager() is
called in AccessibilitySettings.onAttach().

Solution: Mocks the LocalBluetoothManager for tests to successfully
instantiate AccessibilityHearingAidPreferenceController to prevent null
pointer exception from happening.

Bug: 269407238
Test: atest AccessibilitySettingsTest
Change-Id: Ibcfffa10b46fd6e85c1b74b03343e5ee0e8843b3