Introduce VibrationSession to VibratorManagerService

Introduce new interface to represent a generic vibration session, in
preparation for the support for vendor vibration sessions.

Move Vibration CallerInfo, DebugInfo and Status classes to the new
session, since these concepts will be referring to sessions instead of a
single vibration playback.

Migrate ExternalVibration to use the new interface, preserving the
behavior.

Bug: 345414356
Test: VibratorManagerServiceTest
Flag: EXEMPT refactor
Change-Id: Ic184ad77af7e4fde5fa5458744e7b50c5be0a9d4