Add 36 to type scale and swap headings to use it

[edwardhorsford]

Description

In our typography scale, the large size seems smaller than necessary. On GOV.UK it's 36px, whereas in NHS it's 32px. Once our heading guidance is updated, we may see more headings using the large size, so I am proposing updating our type scale to use 36px rather than 32px.

The GOV.UK scale goes:

• Desktop: 24px > 36px > 48px
• Mobile: 21px > 27px > 32px

NHS:

• Desktop: 24px > 32px > 48px
• Mobile: 20px > 24px > 32px

To swap the size would likely be a breaking change - users may be relying on the .nhsuk-u-font-size-32 classes or passing 32 to the font mixins.

I am proposing adding 36 to the scale and updating the heading mixins to use it, and leave 32 for now. We can then remove 32 from the scale at the next major version.

Mobile before	Mobile after

Desktop before	Desktop after

Scale mobile	Scale desktop

Checklist

• Tested against our testing policy (Resolution, Browser & Accessibility)
• Follows our coding standards and style guide
• CHANGELOG entry