add getBoxSize() for imagick

In addition to #165 it would be great if `imagick` also supports this method.

src/Intervention/Image/Imagick/Font.php

@@ -75,4 +75,44 @@ class Font extends \Intervention\Image\AbstractFont
         // apply to image
         $image->getCore()->annotateImage($draw, $posx, $posy, $this->angle * (-1), $this->text);
     }
+    
+    /**
+     * Calculates bounding box of current font setting
+     *
+     * @return array
+     */
+    public function getBoxSize()
+    {
+        $box = [];
+
+        // build draw object
+        $draw = new \ImagickDraw();
+        $draw->setStrokeAntialias(true);
+        $draw->setTextAntialias(true);
+
+        // set font file
+        if ($this->hasApplicableFontFile()) {
+            $draw->setFont($this->file);
+        } else {
+            throw new \Intervention\Image\Exception\RuntimeException(
+                "Font file must be provided to apply text to image."
+            );
+        }
+
+        $draw->setFontSize($this->size);
+
+        $dimensions = (new \Imagick())->queryFontMetrics($draw, $this->text);
+
+        if (strlen($this->text) == 0) {
+            // no text -> no boxsize
+            $box['width'] = 0;
+            $box['height'] = 0;
+        } else {
+            // get boxsize
+            $box['width'] = intval(abs($dimensions['textWidth']));
+            $box['height'] = intval(abs($dimensions['textHeight']));
+        }
+
+        return $box;
+    }
 }