UX: Prevent some composer buttons from receiving focus (PR #12719)

On mobile, pressing any button in the composer area will add focus to the button and remove the software keyboard. This cause a fair bit of jumping in the layout, because we rely on the presence (or not) of the software keyboard to determine the height of the composer area.

This fix adds a preventFocus parameter to the d-button helper. When used, it stops the button element from receiving focus.


while we are at it, I’m unsure why we have a next and not a schedule(“afterRender”) here