Moving <NuxtLayout> to a built-in component

[pi0]

(internally discussed within team meeting)

Allow using NuxtLayout directly in app.vue:

<!-- app.vue -->
<NuxtLayout>
  <NuxtPage/>
</NuxtLayout>

For transition support, NuxtPage needs to communicate with layout. For this we can make use of a global layout state:

const layout = useLayout()
setLayout('welcome') // Only supported before rendering
// Same as useLayout().value = 'welcome'

The limitation is that layout can be only modified before or after rendering lifecycle (in plugins or client-side after mount)

[pi0]

nuxt/framework#3011 partially resolved this issue.