Taskbar in overview

- Behind ENABLE_TASKBAR_IN_OVERVIEW which is disabled by defualt
- Make taskbar unstashed in overview with background visible
- Ensure taskbar is touchable in overview

Bug: 245320601
Test: Home<->Overview, Home<->App, App<->Overview, Home->Overview->App->Home, Home->App->Overview->Home, Overview->Home->App->Overview, Overview->App->Home->Overview, App->Overview->Home->App, App->Home->Overview->App
Test: Go to AllApps, call KEYCODE_HOME, go to app and taskbar should be there
Test: App->Overview->Select->Home->App
Test: QuickSwitch -> App
Test: Repeat above with ENABLE_TASKBAR_IN_OVERVIEW x taskbarStashed on/off
Test: Repeat above with gesture and 3-button
Change-Id: Ib25d68f68e89564851b226536e456d0b2f6306f8

src/com/android/launcher3/DeviceProfile.java

@@ -43,6 +43,7 @@ import androidx.annotation.Nullable;
 
 import com.android.launcher3.CellLayout.ContainerType;
 import com.android.launcher3.DevicePaddings.DevicePadding;
+import com.android.launcher3.config.FeatureFlags;
 import com.android.launcher3.icons.DotRenderer;
 import com.android.launcher3.icons.IconNormalizer;
 import com.android.launcher3.model.data.ItemInfo;
@@ -1276,7 +1277,10 @@ public class DeviceProfile {
             return ((taskbarSize - overviewActionsHeight) / 2) + getTaskbarOffsetY();
         }
 
-        return isTaskbarPresent ? stashedTaskbarSize : mInsets.bottom;
+        if (isTaskbarPresent) {
+            return FeatureFlags.ENABLE_TASKBAR_IN_OVERVIEW.get() ? taskbarSize : stashedTaskbarSize;
+        }
+        return mInsets.bottom;
     }
 
     /** Gets the space that the overview actions will take, including bottom margin. */

src/com/android/launcher3/config/FeatureFlags.java

@@ -238,6 +238,10 @@ public final class FeatureFlags {
             "ENABLE_ALL_APPS_ONE_SEARCH_IN_TASKBAR", false,
             "Enables One Search box in Taskbar All Apps.");
 
+    public static final BooleanFlag ENABLE_TASKBAR_IN_OVERVIEW = getDebugFlag(
+            "ENABLE_TASKBAR_IN_OVERVIEW", false,
+            "Enables accessing the system Taskbar in overview.");
+
     public static final BooleanFlag ENABLE_SPLIT_FROM_WORKSPACE = getDebugFlag(
             "ENABLE_SPLIT_FROM_WORKSPACE", true,
             "Enable initiating split screen from workspace.");