Simplify android:gravity in two layouts (#6506)

The "Inspect Code" linter complained that these two files
had Right-to-left text compatibility issues. I couldn't
really see any problems neither in English nor in Hebrew,
but the linter's suggestion still made sense, so I cleaned it up.

This fixes all the errors of the type
"Android Lint: Internationalization / Right-to-left text compatibility issues".

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

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

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

@@ -16,7 +16,7 @@
     android:padding="12dp"
     app:layout_constraintEnd_toEndOf="parent"
     app:layout_constraintStart_toStartOf="parent"
-    app:layout_constraintTop_toTopOf="parent"></EditText>
+    app:layout_constraintTop_toTopOf="parent" />
 
   <TextView
     android:id="@+id/recent_searches"

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

@@ -22,9 +22,8 @@
         android:id="@+id/tv_review_question"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
-        android:gravity="center_vertical"
+        android:gravity="center"
         tools:text="testing1"
-        android:textAlignment="center"
         android:textColor="?attr/reviewHeading"
         android:textSize="32sp"/>
 
@@ -33,9 +32,8 @@
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_marginBottom="@dimen/filter_padding"
-        android:gravity="center_vertical"
+        android:gravity="center"
         tools:text="testing2"
-        android:textAlignment="center"
         android:textSize="22sp"/>
 
     </LinearLayout>

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

@@ -119,7 +119,7 @@
                       android:layout_width="match_parent"
                       android:layout_height="match_parent"
                       android:layout_weight="1"
-                      android:orientation="horizontal"></LinearLayout>
+                      android:orientation="horizontal" />
 
                     <LinearLayout
                       android:id="@+id/ll_location_status"

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

@@ -35,7 +35,6 @@
         android:layout_height="wrap_content"
         android:id="@+id/appwidget_title"
         android:textAlignment="center"
-        android:layout_gravity="bottom"
         android:textColor="@color/white"
         android:layout_marginTop="@dimen/filter_padding"
         android:layout_marginStart="@dimen/tiny_padding"