EPIC: Make typography more accessible - in line with GOV

[sarawilcox]

GOV.UK is making the GOV.UK Frontend typography scale more accessible. See their Design System blog post.
We may want to follow suite to stay aligned with GOV.

https://designnotes.blog.gov.uk/2022/12/12/making-the-gov-uk-frontend-typography-scale-more-accessible/

[sarawilcox]

Tie this up with the review of H3 and H4 headings: nhsuk/nhsuk-service-manual-community-backlog#445

[Moll-Lee]

We should move this ticket into the later column as it has a direct dependency on other work we are completing around potentially becoming more aligned with Gov.UK which will include the above,

[sarawilcox]

May be dependent on EPIC: Explore rebuilding NHS.UK frontend directly from GOV

[edwardhorsford]

I've raised a PR to add guidance about heading sizes and when to use which.