[Enhancement] New heading style - H4

[x] I have written a good issue

Describe the enhancement

In the design library (Sketch) we have the possibility to make a Section header in font size 16 - bold. To align and support this in Kirby code, we could define a new heading size "H4" with font size 16 - bold.

Describe the solution you'd like

Define new text style "H4"

font-size: font-size("n");
font-weight: font-weight("bold");
CLASS: h4 or kirby-text-medium

Add this new text style to the "Fonts" page on the Cookbook

05 P

https://cookbook.kirby.design/#/home/showcase/fonts

Have you considered any alternatives?

Are there any additional context?

Checklist:

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Refinement

[ ] Request that the issue is UX refined; do not proceed until this is done.
[ ] Request that the issue is tech refined; do not proceed until this is done.

Implementation

The contributor who wants to implement this issue should:

[ ] Make sure you have read: "Before you get coding".
[ ] Signal to others you are working on the issue by assigning yourself.
[ ] Create a branch from the develop branch following our branch naming convention.
[ ] Publish a WIP implementation to Github as a draft PR and ask for feedback.
[ ] Make sure you have implemented tests following the guidelines in: "The good: Test".
[ ] Update the cookbook with examples and showcases.

Review

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[ ] Do a self-review.
[ ] Create a pull-request. If you created a draft PR during implementation you can just mark that as "ready for review".

kirbydesign / designsystem