129964: Fixed the header role structure being invalid in the custom theme

- Replaced the menubar role from the parent of all the header buttons like lang switch, auth menu & help toggle with toolbar
- Replaced the remaining `<a>` buttons in the header with `<button>` to make them expandable with space
- Fixed accessibility issues flagged by axe DevTools in the user menu dropdown

src/app/shared/log-in/methods/password/log-in-password.component.html

@@ -35,11 +35,11 @@
     <div class="mt-2">
       @if (canRegister$ | async) {
         <a class="dropdown-item" [routerLink]="[getRegisterRoute()]"
-        [attr.data-test]="'register' | dsBrowserOnly" role="menuitem" tabindex="0">{{"login.form.new-user" | translate}}</a>
+        [attr.data-test]="'register' | dsBrowserOnly" tabindex="0">{{"login.form.new-user" | translate}}</a>
       }
       @if (canForgot$ | async) {
         <a class="dropdown-item" [routerLink]="[getForgotRoute()]"
-        [attr.data-test]="'forgot' | dsBrowserOnly" role="menuitem" tabindex="0">{{"login.form.forgot-password" | translate}}</a>
+        [attr.data-test]="'forgot' | dsBrowserOnly" tabindex="0">{{"login.form.forgot-password" | translate}}</a>
       }
     </div>
   }