avoid code duplication in page components

[fago]

When adding multiple page components, as done since #290, there are quite some duplicate code parts in the setup helper. Let's provide some composables to void this code duplication.

[fago]

Suggestion:

1. Move layout handling out from page component to layout.vue - so it's centralized and we avoid duplication. Usually all pages have the same layout. That's a good default and if it's not fitting, projects are free to move it over / back to pages.

app.vue

<template>
 <NuxtLayout :name="useDrupalCe().getPageLayout()">
   <NuxtPage />
 </NuxtLayout>
</template>

We need to make the page parameter to getPageLayout optional and default to useDrupalCe().getPage() if not given to make it this short.

2. Simplify page component code to this, by introducing a new helper: usePageHead()

<template>
  <main>
    <SiteBreadcrumbs />
    <DrupalTabs v-if="page.local_tasks" :tabs="page.local_tasks" />
    <component :is="renderCustomElements(page.content)" />
  </main>
</template>

<script lang="ts" setup>
const { fetchPage, renderCustomElements, usePageHead } = useDrupalCe()
const page = await fetchPage(useRoute().path, { query: useRoute().query })
usePageHead(page)
</script>

[fago]

layout handling has test-coverage already, but metadata handling has not. thus added it: #295

[vloss3]

1. the fetchPage request to find layout happens after app.vue is rendered so I don't think it would work, but agree that NuxtLayout in app.vue is unnecessary, we can keep it in pages only
2. looks good