Add a flow that can be used to determine whether cross window blur is enabled/supported right now.

CrossWindowBlurListeners handles the following checks for blur:
 1. whether the device supports blur or not (ro.surface_flinger.supports_background_blur property)
 2. whether battery saver is enabled or not
 3. whether critical thermal status has reached or not
 4. whether blur is disabled in dev settings or not
 5. whether multimedia tunneling is enabled or not.

Repository adds two additional checks:
 1. whether persist.sysui.disableBlur is set or not (used by tests)
 2. whether ActivityManager.isHighEndGfx is true or not, BlurUtils has this check before enabling or disabling blur.

Bug: 391409723
Test: Tried adding unit tests but it might be flakey because of ActivityManager.isHighEndGfx check, it is unclear how this can be mocked
Flag: com.android.systemui.bouncer_ui_revamp
Change-Id: Ie4ec36e132fef04a40bd3e0c054065554be1b302