Fix vertical gap in resize bar (#1917)

Author: MortimerGoro

app/src/main/res/drawable/resize_bar_background.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<shape android:shape="rectangle" xmlns:android="http://schemas.android.com/apk/res/android">
+    <solid android:color="@color/asphalt" />
+    <corners android:radius="20dp"/>
+</shape>

app/src/main/res/layout/navigation_bar_resize.xml

@@ -7,6 +7,7 @@
         android:layout_height="wrap_content"
         android:layout_gravity="center"
         android:orientation="horizontal"
+        android:background="@drawable/resize_bar_background"
         android:visibility="gone">
 
         <org.mozilla.vrbrowser.ui.views.UITextButton