fix(virtual-node): default and lowercase type property

[straker]

Allows us to do input property matches with case insensitivity for serial and virtual nodes.

const input = document.createElement('input');
input.setAttribute('type', 'BUTTON');
const vNode = axe.utils.getFlattenedTree(fixture)[0];

commons.matches(vNode, {
  properties: {
    type: 'button'
  }
}); // true

const serialNode = new axe.SerialVritualNode({
  nodeName: 'input',
  attributes: {
    type: 'BUTTON'
  }
});

commons.matches(serialNode, {
  properties: {
    type: 'button'
  }
}); // true

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Resolved