Fix Vibrator and VibratorManager public API docs

Add information about value returned by Vibrator.getId, including a
description of what the default -1 value represents.

Fix description of CombinedVibrationEffect arguments to
VibratorManager methods.

Fix: 180962151
Fix: 180963421
Test: N/A
Change-Id: I3fab2d5fe299be5a951f32bd75eb2e5275ef6e56