Refactor Single key detector to provide start, complete and cancel

This is just a refactor internally to provide this capability, we
only use COMPLETE events which behave exaclty like the current
behaviours.

The reason was to provide ways to listen to START, COMPLETE and
CANCEL events for certain key gestures (e.g. Gemini animation when
long press POWER occurs). This would be as a subsequent CL.

Flag: EXEMPT refactor
Bug: 358569822
Test: atest WmTests
Change-Id: Icc987173564e5675629731b99b02aa7e3c10015b