Update Kirigami tutorial

Only minor blockers now, they should be done by the end of the month:

• Remove org::kde::kirigami:: section of certain links
• Lessen the use of API links where not needed (e.g. form layout instead of FormLayout) (Style: should follow max of 1 of the same API link in the same paragraph)
• Fix some page weights (style pages)
• Remove excessive comments and add where needed/relevant
• Add alternative text for accessibility
• Check which images should use the {{< figure >}} shortcode
• Move ListModel functions to introduction-listviews (it's actually fine where it is)
• Retroactively check if there are still code examples using tabs instead of 4 spaces (introduction-actions?)
• Add more beginner C++ resources
• Test Kirigami gallery
• Recheck style-colors to mention qqc2-breeze-style and qqc2-desktop-style (Does not concern app developers)
• Confirm that PageRow links work
• Check what needs to be done with deprecated ItemViewHeader in components-listviews (full deletion, removed from KF6)
• Check every code example for correctness and buildability

Important reminders:

• See if there's a friendlier way to implement the singleton in about-page
• Write a STYLE.md guide for this repo's readme (e.g. avoid API links abuse, introduction to the API by mentioning namespace etc)
• Document {{< sections >}} and {{< compare >}} shortcode in this repo's readme, consider moving most of it to CONTRIBUTING.md

Self-hosted version for previewing the results: http://vps22927.publiccloud.com.br:6789/docs/use/kirigami/

To test this MR:

git clone https://invent.kde.org/documentation/develop-kde-org.git
cd develop-kde-org
git mr 235
hugo server