Create a WCT to set task non-trimmable.

In some scenarios, like transparent wallpaper case for dw we need to set
task to non-trimmable to prevent recents from trimming it.

Bug: 345617792
Test: Manually verify that wallpaper does not get removed when swiping
up to overview after quickswitching
Flag: com.android.window.flags.enable_desktop_windowing_wallpaper_activity

Change-Id: I4e3fbfaf4284136257b82cce715d04aac4d0cf41