st/theme-node: Default to right text-align in RTL

When neither the theme node itself nor any of its parents specifies
an explicit text direction, we default to aligning to the left.

That's a good default for LTR locales, but for RTL aligning to the
right is a better one.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2247>

src/st/st-theme-node.c

@@ -2649,6 +2649,9 @@ st_theme_node_get_text_align(StThemeNode *node)
     }
   if(node->parent_node)
     return st_theme_node_get_text_align(node->parent_node);
+
+  if (clutter_get_default_text_direction () == CLUTTER_TEXT_DIRECTION_RTL)
+    return ST_TEXT_ALIGN_RIGHT;
   return ST_TEXT_ALIGN_LEFT;
 }