Add isVisible to Task

This is needed to determine whether a running task in Desktop is
minimized.

Also revert ag/27144586 to now include minimized tasks in
getRecentTasks().

Bug: 333872717
Bug: 315354060
Flag: com.android.launcher3.enable_recents_in_taskbar
Test: RecentTasksControllerTest + see other CLs in topic
Change-Id: I9631cc28ead4437ecf6e4689b839e14674c429cc