Fix inconsistencies of TextareaWidget and TextareaWithSummaryWidget form elements

Coming from #2421445-30: Text format wrapper does not honor description_display → . To fix that bug, I wanted to entirely remove some code that lives in the wrong templates, yet it includes a @see comment pointing here. 😅 During self-review (#30.4) I pointed out the brokenness of attributes not being used in the wrapper element. Now that I'm reading the summary here, that's most of what this issue aims to fix. Hopefully this will be smaller and easier to land once we get the description out of the way entirely and leave that to form-element.html.twig itself (when {{ children }}is rendered).

I won't formally mark this postponed, but it should probably wait until #2421445 lands...