Replace taskbar hotseat with real hotseat when folder is open

- Seamlessly show real hotseat and hide taskbar hotseat, while
  keeping rest of taskbar visible
- Update MultiValueAlpha to allow for taking max alpha instead
  of blending, and use that for Hotseat
- Fix folder open bounds on home screen when taskbar is present

Test: Open folder from taskbar on home, can drag out items
Bug: 182079330
Bug: 171917176
Change-Id: I7c1983e3219b1341cf233260f0ccac9051c4dc14

quickstep/src/com/android/launcher3/BaseQuickstepLauncher.java

@@ -315,6 +315,10 @@ public abstract class BaseQuickstepLauncher extends Launcher
     @Override
     public void onDragLayerHierarchyChanged() {
         onLauncherStateOrFocusChanged();
+
+        if (mTaskbarController != null) {
+            mTaskbarController.onLauncherDragLayerHierarchyChanged();
+        }
     }
 
     @Override