Add support for wearable hotword.

Add the ability for a wearable device connected to WearableSensingService to trigger a (second-stage) hotword detection on the HotwordDetectionService on the phone and forward the result and audio stream to the AlwaysOnHotwordDetector if detected.

Bug: 310055381
Test: Verified data flow between WearableSensingService, HotwordDetectionService, and AlwaysOnHotwordDetector on device. Also added CTS tests to test several end-to-end behaviors in HotwordDetectionServiceBasicTest.

Change-Id: I51d4ad3f80e463729c183c87962cc9205e52ba21