Remove all external usages of GroupTask.task1/2 from Launcher3

See go/refactor-group-task for details. This CL removes all the usages
of `task1` and `task2` from `GroupTask` in Launcher3. Follow-up CLs will
remove it from NexusLauncher and remove the fields altogether.

Bug: 388593902
Test: m
Flag: EXEMPT pure refactor with no behavior change.
Change-Id: I902c8135b3a0aae95acf25267b3bcbf286bd4e7d

quickstep/src/com/android/launcher3/taskbar/KeyboardQuickSwitchController.java

@@ -233,7 +233,8 @@ public final class KeyboardQuickSwitchController implements
     }
 
     private boolean shouldExcludeTask(GroupTask task, Set<Integer> taskIdsToExclude) {
-        return Flags.taskbarOverflow() && taskIdsToExclude.contains(task.task1.key.id);
+        return Flags.taskbarOverflow() && task.getTasks().stream().anyMatch(
+                t -> taskIdsToExclude.contains(t.key.id));
     }
 
     private void processLoadedTasks(List<GroupTask> tasks, Set<Integer> taskIdsToExclude) {