Mark minimized Recents tasks in GroupedRecentTaskInfo.java and Task.java

With this CL we mark Recent Desktop tasks so that SystemUI / Launcher
can know which tasks are minimized.

Note: when we're in desktop mode it is enough to know whether a desktop
task is visible to know whether it is minimized. However, when outside
desktop mode (e.g. in Overview) all desktop tasks are marked invisible
so we need to have a separate field to know whether a task is minimized.

Bug: 333013317
Flag: com.android.window.flags.enable_desktop_windowing_mode
Test: manual: ensured minimized desktop tasks are not shown in Overview

Change-Id: I9011676234762a9b81d0df84c300fea05f6df442