Various fixes for html-validate (nested forms etc)

[colinrotherham]

PR to fix various issues flagged by html-validate which we've temporarily ignored

Issues now fixed

• Some pages have nested <form> elements #2609
• Navigation toggle buttons had implicit type="submit"
• Some HTML attributes used single quotes

To fix "forms within forms" I've split our example layout in two:

1. Use layout-example.njk for examples without forms
2. Use layout-example-form.njk for examples with forms

Issues already fixed

Plus some issues had already been fixed so we can remove their rules:

• Status tags in headings are invalid HTML #2606
• Set the boolean disabled attribute consistently in the button component govuk-frontend#2830

I'll open a separate PR for cookie banner specific things

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[36degrees]

Generally looks good but I don't quite understand the changes or the commit message for d540a4e – alphagov/govuk-frontend#2830 is part of v5 so that fix hasn't gone out yet?

[colinrotherham]

Generally looks good but I don't quite understand the changes or the commit message for d540a4e – #2830 is part of v5 so that fix hasn't gone out yet?

@36degrees Ahh in that case, maybe we fixed them all here too?

We have failures for <fieldset hidden=""> but can't find any <button disabled="disabled"> anymore

Comes from where we pass an empty string into the attribute value:

govuk-design-system/src/cookies.njk

Lines 115 to 118 in 8821a80

	attributes: {
	id: "analytics",
	hidden: ""
	}

Remember this?

• Add support for HTML5 boolean attributes govuk-frontend#1665

I'll update the example again

[36degrees]

Realised we don't have any examples of disabled buttons so I suspect the rule was always disabled because of the hidden attribute on fieldsets? 🤔 Anyway, the comment change still makes sense.

[colinrotherham]

Realised we don't have any examples of disabled buttons so I suspect the rule was always disabled because of the hidden attribute on fieldsets? 🤔 Anyway, the comment change still makes sense.

@36degrees Great, thanks

Yeah. Possibly just copied over from alphagov/govuk-frontend@500a02f