fix(jsx): JSX.Element extends VNode

[KaelWD]

JSX is compiled to createVNode calls, so should be compatible with functions that accept VNode. The functional component tests were invalid because components should return VNodes, I had to add h overloads for Text nodes to keep the same functionality.

[07akioni]

Has anyone reviewed the PR? I've met the problem and hope not to write <xxx /> as VNode.