Add guidance to the text input component to help users understand when to use input type="number"

[36degrees]

What

Add guidance to help users understand when it's appropriate to use input type="number"

Why

We have a lot of research that shows that input type="number" can be problematic and we believe that it should only be used in very specific contexts.

Done when…

• We understand whether there are valid use cases for using input type="number" that outweigh the negatives (usability and accessibility issues)
• We've drafted guidance to add to the Design System to help users understand when they should use it; when not; and what they should use instead
• We've updated the html and nunjucks examples
• Guidance 2i'd
• Guidance published
• Old url retired and redirected

[StephenGill]

Suggested update to text-input guidance here: https://docs.google.com/document/d/1waXRg1DrwZgMVEQJkjLyNQ2bK5beatTcZPRxNekETtI/edit

Needs a review for accuracy from @hannalaakso

[hannalaakso]

Thanks @StephenGill this is a great start! There's a lot to talk about when it comes to type="number" so maybe we should write the blog post first and then distil this content from there...