Move NavButtons to end of taskbar

* Layout hotseat icons from the end instead of the start
* IME down and system back arrow are now separate views

Bug: 191399224
Test: Tested w/ RTL + LTR in gesture
and 3 button nav w/ and w/o IME

Change-Id: I4d0ecd0bee0c519892c63eeefef45055b26d349b
diff --git a/quickstep/res/layout/taskbar.xml b/quickstep/res/layout/taskbar.xml
index dfa17d6..c0e0862 100644
--- a/quickstep/res/layout/taskbar.xml
+++ b/quickstep/res/layout/taskbar.xml
@@ -36,18 +36,27 @@
         android:layout_height="wrap_content"
         android:layout_gravity="bottom" >
 
+        <FrameLayout
+            android:id="@+id/start_contextual_buttons"
+            android:layout_width="wrap_content"
+            android:layout_height="match_parent"
+            android:paddingLeft="@dimen/taskbar_nav_buttons_spacing"
+            android:paddingRight="@dimen/taskbar_nav_buttons_spacing"
+            android:gravity="center_vertical"
+            android:layout_gravity="start"/>
+
         <LinearLayout
-            android:id="@+id/start_nav_buttons"
+            android:id="@+id/end_nav_buttons"
             android:layout_width="wrap_content"
             android:layout_height="match_parent"
             android:orientation="horizontal"
             android:paddingLeft="@dimen/taskbar_nav_buttons_spacing"
             android:paddingRight="@dimen/taskbar_nav_buttons_spacing"
             android:gravity="center_vertical"
-            android:layout_gravity="start"/>
+            android:layout_gravity="end"/>
 
         <FrameLayout
-            android:id="@+id/end_nav_buttons"
+            android:id="@+id/end_contextual_buttons"
             android:layout_width="wrap_content"
             android:layout_height="match_parent"
             android:paddingLeft="@dimen/taskbar_nav_buttons_spacing"