Add skeleton implementation for Attention API

This service will let the system know whether the user is paying attention to
the device. This may be useful in certain scenarios - like keeping the screen
on, even when there has been no touch related user activity.

New permission BIND_ATTENTION_SERVICE is added to ensure that only the system
can bind to the attention service.

Test: manually tested the lifecycle is as expected
Bug: 111939367
Change-Id: I2dab9c69f3d0c6efb0db572f797f517dc6efcc72