Extract Vibrator implementation from interface.

Moved the core logic of Vibrator into SystemVibrator, potentially
allowing for the creation of other Vibrator subclasses.

Fixed several places where we were creating new Vibrator
instances unnecessarily instead of getting it from the Context.

It is safe to make Vibrator abstract because its constructor
was hidden from the SDK so it was not possible to subclass it.

Bug: 6334179
Change-Id: I18ece6544c26a7efb2d5099f8346a10aef8a5e18