Add executors to handle binder call.

Use background executor to handle TelecomManager#IsInCall binder call
and LockpatternUtils#isSecure which can sometimes lead to binder call.

Also added a unit test file.

Fixes: 266482108
Test: Unit test and interact with emergency button on bouncer. Observe
its visibility.

Change-Id: If590f39ebdc622a89d7de36becff973bf116e355