Create listener for dynamic blurEnabled changes

This CL exposes an API to let apps know when the blur has been enabled
or disabled dynamically.

This could be due to battery saving mode turned on, tunnel mode being
used, minimal post processing requested, etc.

This adds a WindowManager.addCrossWindowBlurEnabledListener, which allows
apps to add/remove a listener for blur enabled state changes. The
listeners are registered in a CrossWindowBlurListeners, which receives
updates from WindowManagerService when blurEnabled changes.
CrossWindowBlurListeners only registers a remote listener if the client
initializes it. I.e. if the app is not interested in blurs, the
CrossWindowBlurListeners won't get initialized and won't register a
remote listener.

WindowManagerService holds a RemoteCallbackList, which holds listeners
for each client process and notifies them when there are updates. If any
of the listeners' process dies, the entry is removed from the list.

Bug: 177524486
Test: m
CTS-Coverage-Bug: 179990440
Change-Id: I3fe8f2d2008171d6b069e8ee6f3b47e5b5d60cfa