Ensure tabListSlot is display block if its the role=tablist

By default tabListSlot is `display:contents` which can cause a couple of
issues:

 1. Some browsers don't expose role information for elements that are
    display:contents, and so this makes an inaccessible component.
 2. Depending on how the tabs are styled, they can end up in weird
    orientations due to the tablist having no layout. Making it have a
    layout with display:block fixes this.

Author: keithamus

src/tab-container-element.ts

@@ -186,12 +186,14 @@ export class TabContainerElement extends HTMLElement {
 
   selectTab(index: number): void {
     if (!this.#setup) {
+      const tabListSlot = this.#tabListSlot;
       const customTabList = this.querySelector('[role=tablist]')
       if (customTabList && customTabList.closest(this.tagName) === this) {
-        this.#tabListSlot.assign(customTabList)
+        tabListSlot.assign(customTabList)
       } else {
-        this.#tabListSlot.assign(...[...this.children].filter(e => e.matches('[role=tab]')))
-        this.#tabListSlot.role = 'tablist'
+        tabListSlot.assign(...[...this.children].filter(e => e.matches('[role=tab]')))
+        tabListSlot.role = 'tablist'
+        tabListSlot.style.display = 'block'
       }
       const tabList = this.#tabList
       if (this.hasAttribute('aria-description')) {