draft: Add 'Layouts' page

[janfaracik]

An early attempt at some guidance on the various layouts Jenkins supports.

Would be great to get thoughts/ideas/contributions 👍

⚠️ App bars don't work correctly at the moment the way the Design Library uses them, this will be fixed

[janfaracik]

Looks really good, is it worth having child pages of this that has actual rendered examples?

Good idea! I've updated the code component to include a button to open the preview in a new tab. The way it works isn't ideal (lots of code duplication) but it's a start.

[timja]

any reason this is still in draft?

[janfaracik]

any reason this is still in draft?

There's a change to core I need to make relating to app bars first (small change to their placement in code), wanting to cut down on existing PRs first just to reduce mental load before opening it.

[janfaracik]

Happy to give this a tick @timja and I'll merge it?

[janfaracik]

doesn't jenkins.version in pom.xml need to be 2.374?

Ah yes it'll need to be the weekly the app bar change was merged in, otherwise each page will lack a heading.

v2.371