[android] Add content description for customisable left button

Signed-off-by: Harry Bond <me@hbond.xyz>

android/app/src/main/java/app/organicmaps/maplayer/MapButtonsController.java

@@ -213,11 +213,13 @@ public class MapButtonsController extends Fragment
       )
       {
         leftButtonView.setImageResource(R.drawable.ic_christmas_tree);
+        leftButtonView.setContentDescription(getString(R.string.help));
         leftButtonView.setOnClickListener((v) -> mMapButtonClickListener.onMapButtonClick(MapButtons.help));
       }
       else
       {
         mLeftButton.drawIcon(leftButtonView);
+        leftButtonView.setContentDescription(mLeftButton.getPrefsName());
         leftButtonView.setOnClickListener((v) -> mLeftButton.onClick(leftButtonView));
       }
       //      else

android/app/src/main/res/layout/map_buttons_help.xml

@@ -4,7 +4,6 @@
   xmlns:app="http://schemas.android.com/apk/res-auto"
   android:id="@+id/help_button"
   style="@style/MwmWidget.MapButton.Square"
-  android:contentDescription="@string/help"
   android:tint="@null"
   app:shapeAppearanceOverlay="@style/MwmWidget.MapButton.Square"
   app:srcCompat="@drawable/ic_question_mark" />