Allow HotwordDetectionService to return HotwordRejectedResult.

This is simply passed through the system to the AlwaysOnHotwordDetector.

Bug: 182788844
Bug: 168305377
CTS-Coverage-Bug: 183425641
Test: builds
Change-Id: I2b7147b330051d870bfe970e9b5e16aaab52e9bc
6 files changed