refactor: move how overlay max-width is set (#192)

Instead of setting max-width: none when a dialog is dragged or
resized directly to the node style attribute, use a custom attribute
which is used in a CSS selector to apply that style. It will prevent
a custom max-width from being reset when user resizes or drags the
dialog.

Author: DiegoCardoso

src/vaadin-dialog.html

@@ -24,6 +24,10 @@
       [part="content"] {
         min-width: 12em; /* matches the default <vaadin-text-field> width */
       }
+
+      :host([has-bounds-set]) [part="overlay"] {
+        max-width: none;
+      }
     </style>
   </template>
 </dom-module>
@@ -395,7 +399,7 @@
 
           if (overlay.style.position !== 'absolute') {
             overlay.style.position = 'absolute';
-            overlay.style.maxWidth = 'none';
+            this.$.overlay.setAttribute('has-bounds-set', '');
             this.__forceSafariReflow();
           }