Add All Apps entry button to Taskbar.

- Opens All Apps when clicked
- Fades button in/out when transitioning b/w Hotseat & Taskbar

Bug: 205803230
Test: manual
      ensures alpha gets reset properly
      clicking button opens all apps
Change-Id: I1b96bae734aa9fd9308931d6312e3d65559d4284
diff --git a/src/com/android/launcher3/InvariantDeviceProfile.java b/src/com/android/launcher3/InvariantDeviceProfile.java
index 0b168a5..a381787 100644
--- a/src/com/android/launcher3/InvariantDeviceProfile.java
+++ b/src/com/android/launcher3/InvariantDeviceProfile.java
@@ -135,7 +135,7 @@
     /**
      * Number of icons inside the hotseat area.
      */
-    protected int numShownHotseatIcons;
+    public int numShownHotseatIcons;
 
     /**
      * Number of icons inside the hotseat area that is stored in the database. This is greater than