GlDropdown: toggle button should keep focus after trigger

When you click on a dropdown toggle button it loses focus and places it on a dropdown list. This is rather confusing because you expect to close this with the same action you've used to open it. Legacy dropdowns don't suffer from this problem.

GlDropdown	Legacy dropdown
Screen_Recording_2022-07-06_at_00.26.42	Screen_Recording_2022-07-06_at_00.29.02