Template hierarchy filter: Preserve existing paths

Instead of solely returning the blade template path locate result, 
append it to the array of existing files passed to the template hierarchy filter handler,
allowing Gutenberg Full Site Editing (FSE) to find and use block templates/template parts in the (Sage 10) theme.

src/Roots/Acorn/Sage/Concerns/FiltersTemplates.php

@@ -14,7 +14,7 @@ trait FiltersTemplates
      */
     public function filterTemplateHierarchy($files)
     {
-        return $this->sageFinder->locate($files);
+        return $files + [$this->sageFinder->locate($files)];
     }
 
     /**