When spreading attributes, the setters of the element are checked. If they contain the key in question, it's set via that setter. For certain setters on certain elements this didn't work because the element prototype was not HTMLElement, rather a descendant of that (for example HTMLDivElement), which meant that only the setters of the descendant, not the superclass were taken into account. This fixes that by walking up the prototype chain until we find the Element prototype.
fixes #11179
