Show desktop tasks when taskbar is pinned on home

Updates taskbar and KQS to show (running) desktop tasks when taskbar is
shown on the home screen - adds `shouldShowDesktopTasksInTaskbar` method
to TaskbarDesktopModeController to be used instead of
`areDesktopTasksVisible*()` to determine whether to show desktop tasks
in the taskbar. The method, in addition to desktop tasks visibility,
also considers whether taskbar should be shown on the home screen, and
whether current launcher state is home.

The launcher state is fetched from `TaskbarStashController`, which
already keeps track of this state. This is likely not ideal, but can be
removed in the long term - see http://b/390665752.

Furthermore, updates ReventsModel login not to always filter out desktop
tasks with no non-minimized tasks (which is currently expected behavior
in overview) in `getTasks()`. The filtering is now done by the filter
passed to `getTasks()` method, instead of when processing tasks in the
background. The filter used by default is updated to filter out such
desktop tasks, but callsites from `KeyboardQuickSwitchController` and
`TaskbarRecentAppsController` are updated to use an empty filter, so
they can display desktop tasks when they're all minimized.

Bug: 376711722
Bug: 390665160
Test: Manual on desktop device - verify that taskbar and KQS when shown
on home screen display desktop tasks, including the case all tasks are
minimized.
Flag: com.android.window.flags.enter_desktop_by_default_on_freeform_displays

Change-Id: Iabc22e20bf64aa9a826b4a5952f1edc6ea639cdc