Focus the first possible element in dialogs

See https://www.woltlab.com/community/thread/316063/

Author: dtdesign

ts/WoltLabSuite/Core/Element/woltlab-core-dialog.ts

@@ -10,6 +10,7 @@
  * @since 6.0
  */
 
+import { tabbable } from "tabbable";
 import DomUtil from "../Dom/Util";
 import { adoptPageOverlayContainer, releasePageOverlayContainer } from "../Helper/PageOverlay";
 import * as Language from "../Language";
@@ -74,6 +75,11 @@ export class WoltlabCoreDialogElement extends HTMLElement {
 
     adoptPageOverlayContainer(this.#dialog);
     scrollDisable();
+
+    const focusCandidates = tabbable(this.#dialog);
+    if (focusCandidates.length > 0) {
+      focusCandidates[0].focus();
+    }
   }
 
   close(): void {