Make container role=presentation

The current `<tab-container>` is generic role, which is fine except for
it makes for a messier AT than necessary. The `<tab-container>` itself
_is_ a presentational element (the real AT relevant elements are the
tablist, tabs, and panels), so this change makes that explicit by
setting role=presentation to the tab-container.

Author: keithamus

src/tab-container-element.ts

@@ -119,6 +119,12 @@ export class TabContainerElement extends HTMLElement {
     panelSlot.setAttribute('role', 'presentation')
     shadowRoot.replaceChildren(tabListSlot, panelSlot)
 
+    if (this.#internals && 'role' in this.#internals) {
+      this.#internals.role = 'presentation'
+    } else {
+      this.setAttribute('role', 'presentation')
+    }
+
     this.addEventListener('keydown', this)
     this.addEventListener('click', this)
     this.selectTab(