Dropdown: fix accessibility fail

[PatrykMis]

aria-haspopup and aria-expanded attributes must be set for button element or div with role="button" attribute instead of outer div with data-controller="dropdown".

Moreover:

• The links container must have role="menu" defined.
• Each element (link) in the list must have role="menuitem" defined.
• It would be good to set aria-controls, like in the example linked below.

Here is perfectly working Navigation Menu Button Example in accessibility perspective.

Although web developer can manually add aria-controls logic, menu and menuitem rols manually, he/she is not able to easyly move aria-haspopup and aria-expanded attributes (which are set by predefined javascript) to the proper place.

[excid3]

PRs welcome.