Simplify web component helpers

[gordonbrander]

This PR refactors web component helpers to make them simpler and provide better TypeScript types.

const styles = css`
:host {
  display: block;
}

.hello {
  font-weight: bold;
}
`;

const Hello = ({ greeting }: { greeting: string }) => {
  return h('div', { className: "hello" }, text(greeting))
};

component({
  tag: "x-hello",
  styles,
  props: { greeting: "Hello" },
  render: Hello
});