WindowDecor: Pass correct displayId for back key event

TaskOperations object is being created with default display context
so it will provide the default display id only.
It causes that back button is not working on external displays.

Bug: 343265240
Test: Back button on simulated displays.
Test: atest DesktopModeWindowDecorViewModelTests
Change-Id: Ia4772e898dda20fb16ae85f2b2652a17924e9a7c
4 files changed