Add DisplayPowerControllerInterface which will be used as a parent class

for new DisplayPowerController variant to incorporate the refactoring of
updatePowerState

We have introduced a new interface, DisplayPowerControllerInterface, and
the existing DisplayPowerController implements this class. In a
subsequent CL, we will introduce a new variant of DisplayPowerController which will have all
the suggested refactoring changes. We are using a sysprop
"persist.sys.use_new_display_power_controller", with default value 0,
to dynamically decide which variant is to be used.

By default, we will be using the existing DisplayPowerController.
Check the existing value
-> adb shell getprop persist.sys.use_new_display_power_controller // 1
means the new variant is being used, otherwise the old variant
Switch to new variant:
-> adb shell setprop persist.sys.use_new_display_power_controller "1" // Switches to the new
variant. Requries reboot after this

Bug: 241776244
Test: Manual
Test: atest DisplayPowerControllerTest
Change-Id: I314c66f4170996efbff24917608736ac33ff7e9c