[Component Change Request] Improve layout around form inputs

[stevejalim]

The default CSS for form elements could do with a couple of tweaks around error state handling, showing and hiding of form fields when using the newsletter JS from Bedrock and the multi-checkbox layout.

These have been done as part of mozmeao/birdbox, but worth backporting:

https://github.com/mozmeao/birdbox/blob/main/src/css/birdbox-protocol-overrides.scss

Before the tweaks

After the tweaks

[janbrasna]

To recap, if I get it right:

1. the errors should be closer to the actual inputs,
2. checkbox/radio groups should be better separated from the following flow,
3. there is going to be some JS basket logic upstreamed to Protocol, at which point the hide toggle logic must be made compatible? (what's the current status of this one?)

@stevejalim Would you happen to have a live form sample page somewhere? (I'd be interested in the date-time bells and whistles you've added, and also how you group the checkboxes wrt labels × legends or if you use label-sized headings of sorts…)