WindowManager: Send layer priority hint to SurfaceFlinger

Basic algorithm:
if (!isFocused && preferredModeId > 0) -> priority is 2
if (isFocused && preferredModeId == 0) -> priority is 1
if (isFocused && preferredModeId > 0) -> priority is 0
else priority is INT_MAX

See go/sf-generalizing-refresh-rate for master doc, and
https://docs.google.com/document/d/1ozR7UT3AZclsJ6f4NJ4WXYO2eb-GRdv-Q55AYTltZSo
for WM specific document.

Test: Device starts. Observe logs for errors.
Test: Observe printouts on SF side to make sure the correct number gets passed along.
Test: Unit tests for setting priority on Transaction.
Test: Swappy and Messaging app running in split screen. If swappy in focus,
      it gets priority 0, otherwise 2. If Messsging app in focus it gets priority 1,
      otherwise INT_MAX.
Test: Chrome playing video. Chrome Activity gets priority 0.
Test: Expand status bar. Status bar has priority 1.
Test: Application running. Status bar gets an update. Nothing is passed along.

Bug: 142507166
Change-Id: Iea75f63882b173fad089cd4a32a4831b92206797