function protectVTree(vTree) {
  protect(vTree);

  if (vTree.childNodes.length) {
    for (let i = 0; i < vTree.childNodes.length; i++) {
      protectVTree(vTree.childNodes[i]);
    }
  }
}
Ensures that vTree is not recycled during a render cycle. This effectively
allocates a VTree to a DOM node representation for as long as it's needed.

@param {import('./types').VTree} vTree
@return {void}