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/PagedView.java

@@ -289,7 +289,7 @@ public abstract class PagedView<T extends View & PageIndicator> extends ViewGrou
         newPage = Utilities.boundToRange(newPage, 0, getPageCount() - 1);
 
         if (getPanelCount() > 1) {
-            // Always return left panel as new page
+            // Always return left most panel as new page
             newPage = getLeftmostVisiblePageForIndex(newPage);
         }
         return newPage;
@@ -774,7 +774,7 @@ public abstract class PagedView<T extends View & PageIndicator> extends ViewGrou
 
         if (panelCount > 1) {
             for (int i = 0; i < childCount; i++) {
-                // In case we have multiple panels, always use left panel's page scroll for all
+                // In case we have multiple panels, always use left most panel's page scroll for all
                 // panels on the screen.
                 int adjustedScroll = outPageScrolls[getLeftmostVisiblePageForIndex(i)];
                 if (outPageScrolls[i] != adjustedScroll) {