Leave DOM focus on the summary that opened the menu or a filter input
inside the menu. Navigating items with arrow keys should not move focus
away from the input field.

A menu with a filtering input at the top cannot itself be role=menu
because it hides the input from screen readers. The following
relationship is required.

    <details-menu role="none">
      <input>
      <div role="menu" aria-activedescendant="i1">
        <button id="i1" role="menuitem></button>
      </div>
    </details-menu>

Managing focus with aria-activedescendant requires the attribute to be
attached to the role=menu element in order for the focused item to be
announced.

NVDA requires the element with DOM focus to manage the active
descendant. We use summary or an optional input field as the focused
element.

Co-authored-by: Mu-An Chiou <me@muanchiou.com>

Co-authored-by: Mu-An Chiou <me@muanchiou.com>