fix(Menubar): Move shadow root setup to connectedCallback

The custom element spec forbids inspecting children or attaching a
shadow root in the constructor, which prevents the element from being
cloned. Moving the template lookup and shadow root attachment to
connectedCallback aligns Menubar with the other custom elements on
this branch.

Author: tvdeyen

app/views/alchemy/_menubar.html.erb

@@ -114,14 +114,10 @@
 
     <script type="module" data-turbo-eval="false">
       class Menubar extends HTMLElement {
-        constructor() {
-          super()
+        connectedCallback() {
           const template = this.querySelector("template")
           const attachedShadowRoot = this.attachShadow({ mode: "open" })
           attachedShadowRoot.appendChild(template.content.cloneNode(true))
-        }
-
-        connectedCallback() {
           const width = this.bar.offsetWidth
           this.bar.style = `--panel-width: ${width}px; --left-offset: calc(var(--icon-size) + 32px);`
           this.bar.addEventListener("touchstart", this, { passive: false })