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/DeviceProfile.java

@@ -790,7 +790,7 @@ public class DeviceProfile {
         Point padding = getTotalWorkspacePadding();
         // availableWidthPx is the screen width of the device. In 2 panels mode, each panel should
         // only have half of the screen width. In addition, there is only cellLayoutPadding in the
-        // left side of the left panel and the right side of the right panel. There is no
+        // left side of the left most panel and the right most side of the right panel. There is no
         // cellLayoutPadding in the middle.
         int screenWidthPx = isTwoPanels
                 ? availableWidthPx / 2 - padding.x - cellLayoutPaddingLeftRightPx