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
diff --git a/services/vibratorservice/Android.bp b/services/vibratorservice/Android.bp
index b4342bd..e3c254d 100644
--- a/services/vibratorservice/Android.bp
+++ b/services/vibratorservice/Android.bp
@@ -16,6 +16,7 @@
     name: "libvibratorservice",
 
     srcs: [
+        "VibratorCallbackScheduler.cpp",
         "VibratorHalWrapper.cpp",
     ],