Fragment (empty) tag support

Summary

One rule with JSX is that there can only be one top level node in the render tree.

export default class Header extends HTMLElement {

  connectedCallback() {
    this.render();
  }

  render() {
    return (
      <header>
        <nav>...</nav>
      </header>
      <h1>Welcome to my website!</h1>
    );
  }
}

customElements.define('app-header', Header);

Details

The "fragment" wrapping tag convention can effectively act as a pass through tag that wont be part of the rendered output, but helps from a quality of life perspective when authoring JSX

export default class Header extends HTMLElement {

  connectedCallback() {
    this.render();
  }

  render() {
    return (
      <>
        <header>
          <nav>...</nav>
        </header>
        <h1>Welcome to my website!</h1>
      </>
    );
  }
}

customElements.define('app-header', Header);

Start by locating the JSX parsing and rendering entry points responsible for enforcing a single top-level node. Trace how JSX fragments are represented and emitted, then verify that the fragment wrapper is omitted while its children remain in the rendered output. Add or update coverage for the empty fragment syntax shown in the issue.