[SysUI][Floaty] Use KeyGestureEvent to detect power key gestures

* Use KeyGestureEvent callback to detect both single and multiple key
  gesture
* Detect start, complete and cancellation of power key gesture
* Reuse PhoneWindowManager as source of truth for detecting when
  assistant is launched (e.g., not launch if device not setup)
* Remove now unused flows from repository

Bug: 415690177
Bug: 414534881
Bug: 410486292
Test: atest SqueezeEffectRepositoryTest
Test: atest TopLevelWindowEffectsTest
Test: atest SqueezeEffectInteractorTest
Test: Manual, tested on topic "support_gemini_power_key_animation",
effect seems to working as expected
Flag: com.android.systemui.shared.enable_lpp_assist_invocation_effect

Change-Id: I2e312a8d79d33f5c01f0f838873095b4b501b60e