Rename `wm.DeviceStateController.DeviceState` enum

Rename `wm.DeviceStateController.DeviceState` enum to DeviceStateEnum.
This would help us separate `wm.DeviceStateController.DeviceState` enum from `hardware.devicestates.DeviceState`.
This change is necessary as we are going to use both entities named `DeviceState` in the same context, in a follow-up CL.

Bug: 407772602
Test: Check if no unit-tests fail in presubmits
Flag: EXEMPT refactor
Change-Id: Ibb854e2e80ef74c01a49122e0c5d5666001c1eaa