Only print hash code of svg document

It is only relevant for checking whether the underlying document is shared across icons.

property-loader/src/main/java/com/github/weisj/darklaf/properties/icons/DarkSVGIcon.java

@@ -374,7 +374,7 @@ public class DarkSVGIcon
         public String toString() {
             return "SVGDocumentHolder{" +
                     "loaded=" + loaded +
-                    ", svgDocument=" + svgDocument +
+                    ", svgDocument=" + Objects.hash(svgDocument) +
                     ", uri=" + uri +
                     ", visualPadding=" + visualPadding +
                     '}';