New feature “Text and reading options” for SetupWizard, Wallpaper, and Settings (9/n).

- Fine-tune the legacy interface of the LabeledSeekBarPreference
1) If not set any label, the layout should be gone instead of visible. If not gone, the preference will have redundant space.

Bug: 211503117
Test: make -j64 RunSettingsRoboTests ROBOTEST_FILTER=LabeledSeekBarPreferenceTest
Change-Id: Ideea8589e35083eb89495c0eceba38c62b4807a7

res/layout/preference_labeled_slider.xml

@@ -53,10 +53,12 @@
         android:layout_below="@android:id/summary" />
 
     <LinearLayout
+        android:id="@+id/label_frame"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_below="@id/seekbar_frame"
-        android:orientation="horizontal">
+        android:orientation="horizontal"
+        android:visibility="gone">
 
         <TextView
             android:id="@android:id/text1"