[HA Input] Show notification to hint user can change input device when calling

* Listen to phone state 'CALL_STATE_OFFHOOK' and show notification when hearing device is connected
* 'Switch' action button on notification to temporary switch input device
* 'Settings' action button on notification to launch to device details page
* Tap on notification to also bring user to device details page

Bug: 349255906
Test: atest HearingDevicePhoneCallNotificationControllerTest SystemNotificationChannelsTest
Flag: com.android.settingslib.flags.hearing_devices_input_routing_control
Change-Id: Ic4920e2fde5e0c002018b15c2734a3b27b60d038