Move taskbar to be closer to QSB

- Offset taskbar to be halfway between QSB and bottom of the screen.
- Add taskbar translationY state property to animate when going
  between launcher and an app.
- Draw the taskbar background in TaskbarContainerView instead of
  TaskbarView so it stays pinned to the bottom as TaskbarView
  translates up. If we want to have a background behind the
  taskbar on home, this should move back to TaskbarView so that
  the drawing can be shared by mTaskbarViewOnHome.

Test: visually on home screen, translates when entering and
exiting an app

Bug: 182981881
Bug: 171917176
Change-Id: I44f8b2c770074f7f015dcccbc2befd3453811193
diff --git a/src/com/android/launcher3/LauncherState.java b/src/com/android/launcher3/LauncherState.java
index 0c509a1..58df9c8 100644
--- a/src/com/android/launcher3/LauncherState.java
+++ b/src/com/android/launcher3/LauncherState.java
@@ -184,6 +184,10 @@
         return launcher.getNormalTaskbarScale();
     }
 
+    public float getTaskbarTranslationY(Launcher launcher) {
+        return -launcher.getHotseat().getTaskbarOffsetY();
+    }
+
     public float getOverviewFullscreenProgress() {
         return 0;
     }