Write top focused display ID in WindowManagerServiceDumpProto.

Sometimes the focus display is not updated during test because the
inject event between two displays may be too fast, the input window
info may not been applied to InputFlinger yet before second inject
event.
Add top focused display ID in proto so test cases can monitor this.

Bug: 127741025
Bug: 135104079

Test: stress test on
ActivityLifecycleTopResumedStateTests#testTopPositionSwitchAcrossDisplaysOnTap
Also enable DEBUG_FOCUS in InputFlinger and check log to make sure the input
window is updated during tapOnDisplayCenter.

Test: atest WindowInsetsBehaviorTests MultiDisplayPolicyTests
MultiDisplaySystemDecorationTests ActivityLifecycleTopResumedStateTests
Test: atest MultiDisplayKeyguardTests MultiDisplayLockedKeyguardTests

Change-Id: Ie7ca9645553aaa48077a8ccae9a4376cc7d2e0f6