Fix that the preview text in "Text and reading options" page is too small.

Add the default values into respective TextView

Fix: 222413847
Test: manual test
Change-Id: I1da8a6ea08007c8988ae8dcf798f1645128ac906

res/layout/accessibility_text_reading_preview_mail_content.xml

@@ -25,6 +25,7 @@
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:text="@string/accessibility_text_reading_preview_mail_subject"
+        android:textSize="14sp"
         android:textAppearance="?android:attr/textAppearanceMedium" />
 
     <TextView
@@ -33,6 +34,7 @@
         android:layout_height="wrap_content"
         android:paddingBottom="16dp"
         android:paddingTop="11dp"
+        android:textSize="12sp"
         android:text="@string/accessibility_text_reading_preview_mail_from"
         android:textColor="?android:attr/textColorSecondary" />
 
@@ -40,6 +42,7 @@
         android:id="@+id/content"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
+        android:textSize="13sp"
         android:text="@string/accessibility_text_reading_preview_mail_content"
         android:textAppearance="?android:attr/textAppearanceMedium" />
 </LinearLayout>