Add check answers and extended grid

[dashouse]

This PR adds:

A coded example of the 'Check answers' pattern using the 'Summary list' component and the desktop specific grid.

Documents the extended grid on the layout page (needs a review / chat with @amyhupe)

[dashouse]

This needs a <form> tag added to the Check answers example

[govuk-design-system-ci]

You can preview this change here:

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[36degrees]

Totally non-blocking, and I'm aware this is how it was in the existing pattern, but the more I look at it the stranger I find it it is that there are entries for both 'Contact information' and 'Contact details'…

Surely that's just two different ways of saying the same thing?

[36degrees]

This looks ace @dashouse 👌

Picked up on a couple of minor things that could do with being addressed, and I know this needs a review from @amyhupe too.

[amyhupe]

I think this looks really good – nice one @dashouse

None of my comments are blocking and all relate to things which haven't been introduced by this PR, but:

1. I agree with Ollie's comment about changing the button text in the example to "Accept and send" to match the button component guidance.
2. Looking at it now, I think the Licence period entry in the example being the only one with non-realistic example text is a bit unhelpful, is it possible to swap this for a realistic answer?
3. We should remove all the upper case "C"s from mid-sentence mentions of check answers as we no longer follow this convention.

That's all from me.

Thanks