feat: add AbstractVirtualNode for linting

[straker]

Adds a new AbstractVirtualNode class that just throws on all required properties and functions. This ensures anyone who implements a VirtualNode has everything needed to run it through axe.runVirtualRule. I wanted to have it in its own file in the public directory but since the VirtualNode class extends it it needed to be available before declaring the VirtualNode class.

This allows a JSX styled VirtualNode implementation such as:

class VirtualNode extends axe.AbstractVirtualNode {
  constructor(jsxAST, parent) {

    if (jsxAST.type === 'JSXText') {
      this.props = {
        nodeType: 3
      };
      return;
    }

    this.children = [];

    this._attrs = {};
    jsxAST.openingElement.attributes.forEach(attr => {
      this._attrs[attr.name.name] = attr.value.value;
    });

    this.shadowId = undefined;
    this.parent = parent;
    this.props = {
      nodeType: 1,
      nodeName: jsxAST.openingElement.name.name.toLowerCase(),
      id: this._attrs.id,
      type: this._attrs.type
    };
  }

  attr(attrName) {
    return this._attrs[attrName];
  }

  hasAttr(attrName) {
    return !!this._attrs[attrName];
  }

  hasClass(className) {
     // ...
  }
}

NOTE: by throwing in all required properties and functions, any changes that add new properties or functions could potentially break any libraries who have their own VirtualNode implementation which extends the AbstractVirtualNode. Those libraries should be encouraged to pin to specific versions of axe-core in order to not break on new releases to the AbstractVirtualNode class.

Linked issue: #1551

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Resolved

[stephenmathieson]

The TS stuff is still incorrect.

Why don't we remove the TypeScript stuff for now so we can cut a 3.3 release and add it back later on in a patch (eg 3.3.1)?

Removed tyepscript