Updated an expected render by key

[kitsonk]

Enhancement

We have helper functions that allow a developer to update parts of a virtual DOM (e.g. replaceChild, assignChildProperties) which allow selection of the parts of the virtual DOM by index. We should allow the same functionality by specifying a key. For example, you should be able to do:

replaceByKey(node, 'key', replacementNode);
replacePropertiesByKey(node, 'key', replacementProperties);
replaceChildrenByKey(node, 'key', replacementChildren);
assignPropertiesByKey(node, 'key', properties);

[kitsonk]

We should also consider just plain selection by key and index, allowing the return on a child node for further inspection/assertion.