Shutdown hotword detection service when software hotword detector is shutdown

Currently we have AlwaysOnHotwordDetector and
SoftwareHotwordDetector, when the app creates the detector,
it will create a HotwordDetectionConnection to communicate
with HotwordDetectionService.

Problem:
AlwaysOnHotwordDetector will work incorrectly if the app
creates SoftwareHotwordDetector first, then creates
AlwaysOnHotwordDetector later.

A simple flow is that the app created a
SoftwareHotwordDetector and used it. After a while,
the app may want to use AlwaysOnHotwordDetector,
so it will create a new AlwaysOnHotwordDetector.

By the original flow, it only allows to keep one detector,
so the system will shutdown the old
detector(SoftwareHotwordDetector) and create the new
detector(AlwaysOnHotwordDetector).

Because we don't clear the connection when shutdowning
SoftwareHotwordDetector (PS: We clear the connection
when shutdowning AlwaysOnHotwordDetector), it will use the
previous connection when creating the AlwaysOnHotwordDetector.

Root cause:
Because we don't shutdown hotword detection service when
software hotword detector is shutdown, the new creating
AlwaysOnHotwordDetector will use the previous
HotwordDetectionConnection to communicate with
HotwordDetectionService.

Due to the callback in HotwordDetectionConnection is for
SoftwareHotwordDetector, it can not pass the right data
to AlwaysOnHotwordDetector.

Solution:
Shutdown hotword detection service when software hotword
detector is shutdown.

Bug: 195604579
Test: atest CtsVoiceInteractionTestCases
Test: atest CtsVoiceInteractionTestCases --instant
Test: manual - DSP and non-DSP
Change-Id: I999dc4cc9d5ce858127a9b44db261d7abee98929