[Partial Screenshare] Set WindowContainerToken for task capture

The launch cookie of the target task will be provided by SysUI;
convert this to the WindowContainerToken so the ContentRecorder
can capture the correct layer of the hierarchy.

Bug: 235984372
Test: atest WmTests:WindowManagerServiceTests
Change-Id: I52f69cd078dd5b8ba6cb5b1c292423773dbd8123