Remove widget panel

- Remove all usage of LEFT_PANEL_ID and fixed left panel code
- For preview renderer, load screen 0 + screen 1 instead
- Added a split display specific default workspace layout, with a placeholder app to pass test before we implement page pairing(b/196376162)
- Known issue: If screenId 1 is deleted, right panel will disappear from Wallpaepr & Style because there is no screenId 1. Will be resovled after page pairing(b/196376162)

Bug: 175939730
Test: manual and TaplTestsLauncher3#testWorkSpace
Change-Id: Icac1c94165c14a49c17897c45355b6cdc4d87e91

src/com/android/launcher3/model/GridSizeMigrationTaskV2.java

@@ -38,7 +38,6 @@ import com.android.launcher3.InvariantDeviceProfile;
 import com.android.launcher3.LauncherAppState;
 import com.android.launcher3.LauncherSettings;
 import com.android.launcher3.Utilities;
-import com.android.launcher3.Workspace;
 import com.android.launcher3.graphics.LauncherPreviewRenderer;
 import com.android.launcher3.model.data.ItemInfo;
 import com.android.launcher3.pm.InstallSessionHelper;
@@ -214,9 +213,6 @@ public class GridSizeMigrationTaskV2 {
         // Migrate workspace.
         // First we create a collection of the screens
         List<Integer> screens = new ArrayList<>();
-        if (idp.getDeviceProfile(mContext).isTwoPanels) {
-            screens.add(Workspace.LEFT_PANEL_ID);
-        }
         for (int screenId = 0; screenId <= mDestReader.mLastScreenId; screenId++) {
             screens.add(screenId);
         }