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/Workspace.java

@@ -550,9 +550,6 @@ public class Workspace extends PagedView<WorkspacePageIndicator>
         if (!FeatureFlags.QSB_ON_FIRST_SCREEN) {
             return;
         }
-        if (isTwoPanelEnabled()) {
-            insertNewWorkspaceScreen(Workspace.LEFT_PANEL_ID, getChildCount());
-        }
 
         // Add the first page
         CellLayout firstPage = insertNewWorkspaceScreen(Workspace.FIRST_SCREEN_ID, getChildCount());