Create CallbackScheduler for Vibrator HAL callbacks

This scheduler keeps a single thread looping and executing callbacks
after a delay. This mechanism is used to simulate the callbacks that
some Vibrator HALs do not support.

Bug: 153418251
Test: atest libvibratorservice_test
Change-Id: If19481dfe2eca662d33738a11257bd4509fe81ca
13 files changed