Introduce SingleVibrationSession

Create new implementation for VibrationSession for a single vibration
request. Update the vibrator service to use new class for current and
next vibrations, instead of the current representation.

This change should preserve the existing behaviour for vibration checks
and cancellation.

Bug: 345417514
Flag: EXEMPT refactor
Test: FrameworksVibratorServicesTests
Change-Id: Ica459d1d6e92ef52406e12a23f9c93f26fc171bb