Avoid using overloaded native API's for DOMElement

[michael]

For instance in some places we use el.nodeType which in our abstraction returns a string:

...
  getNodeType() {
    switch(this.el.nodeType) {
      case window.Node.TEXT_NODE:
        return "text"
      case window.Node.ELEMENT_NODE:
        return 'element'
      case window.Node.DOCUMENT_NODE:
        return 'document'
      case window.Node.COMMENT_NODE:
        return 'comment'
      case window.Node.PROCESSING_INSTRUCTION_NODE:
        return 'directive'
      case window.Node.CDATA_SECTION_NODE:
        return 'cdata'
      default:
        //
    }
  }

We should consider deprecating these problematic native API's and use explicit getters when possible.

E.g. el.isCdataElement() then it is clear this is custom API with different semantics.

[michael]

We may also want to use symbols for representing node types. E.g.

const { CDATA } = DOMElement.NodeTypes