App Pairs: Implement save, inflate, launch, and delete

This is the third of several patches implementing the App Pairs feature behind a flag.

This patch includes:
- AppPairIcon and associated XML. Actual icon asset is placeholder for now
- Ability to launch split pair on click
- Icon can be moved around, incl. to Taskbar
- App pair can be deleted by dragging to "Remove" drop zone
- Icon persists on Launcher reload

Change-Id: I88aec6fbc814be98f9ef048bbc5af889d0797970
Flag: ENABLE_APP_PAIRS (set to false)
Bug: 274835596
Test: Not included in this CL, but will follow

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

@@ -117,6 +117,7 @@ import com.android.systemui.unfold.updates.RotationChangeProvider;
 import com.android.systemui.unfold.util.ScopedUnfoldTransitionProgressProvider;
 
 import java.io.PrintWriter;
+import java.util.Collections;
 import java.util.Optional;
 
 /**
@@ -992,9 +993,10 @@ public class TaskbarActivityContext extends BaseTaskbarContext {
         if (recents == null) {
             return;
         }
-        recents.getSplitSelectController().findLastActiveTaskAndRunCallback(
-                info.getComponentKey(),
-                foundTask -> {
+        recents.getSplitSelectController().findLastActiveTasksAndRunCallback(
+                Collections.singletonList(info.getComponentKey()),
+                foundTasks -> {
+                    @Nullable Task foundTask = foundTasks.get(0);
                     if (foundTask != null) {
                         TaskView foundTaskView =
                                 recents.getTaskViewByTaskId(foundTask.key.id);