Fix theme picker breaking in RTL mode

- Fix the preview screen.
- Fix the theme option layout.

Screenshot:
LTR: https://screenshot.googleplex.com/BwN8J2VKKg5.png
RTL: https://screenshot.googleplex.com/Fm4WQKKrB8i.png

Test: Manually, see screenshot
Bug: 159093562
Change-Id: I03cd05d3f4c85472a2bdc70b621cb2ad1651404e
diff --git a/res/layout/theme_option.xml b/res/layout/theme_option.xml
index 557d532..379c507 100644
--- a/res/layout/theme_option.xml
+++ b/res/layout/theme_option.xml
@@ -46,7 +46,7 @@
             android:layout_width="@dimen/theme_option_icon_sample_width"
             android:layout_height="@dimen/theme_option_icon_sample_height"
             android:layout_alignParentTop="true"
-            android:layout_alignParentLeft="true"
+            android:layout_alignParentStart="true"
             android:tint="?android:colorForeground"/>
         <ImageView
             android:id="@+id/theme_option_shape"
@@ -54,7 +54,7 @@
             android:layout_height="@dimen/theme_option_shape_sample_height"
             android:layout_alignBottom="@+id/theme_option_icon"
             android:layout_toEndOf="@id/theme_option_icon"
-            android:layout_marginLeft="@dimen/theme_option_sample_margin"/>
+            android:layout_marginStart="@dimen/theme_option_sample_margin"/>
         <TextView
             android:id="@+id/theme_option_font"
             android:layout_width="@dimen/theme_option_font_sample_width"