For #19820 - Add labels for month and year spinners. (#19870)

This follows the guidelines described in
developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/listbox_role

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

@@ -123,6 +123,12 @@
                 android:layout_weight="1"
                 android:orientation="vertical">
 
+                <TextView
+                    android:layout_width="0dp"
+                    android:layout_height="0dp"
+                    android:labelFor="@id/expiry_month_drop_down"
+                    android:text="@string/credit_cards_expiration_date_month" />
+
                 <androidx.appcompat.widget.AppCompatSpinner
                     android:id="@+id/expiry_month_drop_down"
                     android:layout_width="match_parent"
@@ -142,6 +148,12 @@
                 android:layout_weight="0.8"
                 android:orientation="vertical">
 
+                <TextView
+                    android:layout_width="0dp"
+                    android:layout_height="0dp"
+                    android:labelFor="@id/expiry_year_drop_down"
+                    android:text="@string/credit_cards_expiration_date_year" />
+
                 <androidx.appcompat.widget.AppCompatSpinner
                     android:id="@+id/expiry_year_drop_down"
                     android:layout_width="match_parent"

app/src/main/res/values/strings.xml

@@ -1528,6 +1528,10 @@
     <string name="credit_cards_card_number">Card Number</string>
     <!-- The header for the expiration date of a credit card -->
     <string name="credit_cards_expiration_date">Expiration Date</string>
+    <!-- The label for the expiration date month of a credit card -->
+    <string name="credit_cards_expiration_date_month">Expiration Date Month</string>
+    <!-- The label for the expiration date year of a credit card -->
+    <string name="credit_cards_expiration_date_year">Expiration Date Year</string>
     <!-- The header for the name on the credit card -->
     <string name="credit_cards_name_on_card">Name on Card</string>
     <!-- The header for the nickname for a credit card -->