Refactor the logic of HotwordDetectionConnection

The HotwordDetectionConnection controls the communication
with the HotwordDetectionService and handles the detection
of trusted hotword detector. We separate the detection of
trusted hotword detector into HotwordDetectorSession.

It will be more clear to use original single detector to
implement multiple detectors.

Test: atest CtsVoiceInteractionTestCases
Bug: 241041976
Change-Id: Ib13b906fc4fc27f07325ec6faf2f4948627f4492