Changed the attribute merging logic of use tags

This aims to better align the functionality with the spec and behaviour
of other SVG renderers by prioritising referenced element attributes
instead of use tag attributes.
It also prevents width/height/x/y attributes being applied down to avoid
mis-positioning.

Author: ssddanbrown

src/Svg/Tag/UseTag.php

@@ -69,12 +69,18 @@ public function handle($attributes)
             return;
         }
 
-        $attributes = array_merge($this->reference->attributes, $attributes);
+        $mergedAttributes = $this->reference->attributes;
+        $attributesToNotMerge = ['x', 'y', 'width', 'height'];
+        foreach ($attributes as $attrKey => $attrVal) {
+            if (!in_array($attrKey, $attributesToNotMerge) && !isset($mergedAttributes[$attrKey])) {
+                $mergedAttributes[$attrKey] = $attrVal;
+            }
+        }
 
-        $this->reference->handle($attributes);
+        $this->reference->handle($mergedAttributes);
 
         foreach ($this->reference->children as $_child) {
-            $_attributes = array_merge($_child->attributes, $attributes);
+            $_attributes = array_merge($_child->attributes, $mergedAttributes);
             $_child->handle($_attributes);
         }
     }