How to render headmatter data in custom layout? Missing docs or feature, not sure which one.

[barrymichaeldoyle]

Is your feature request related to a problem? Please describe.
I would like to use headmatter data inside my custom layout but there isn't any documentation on how this can be done.

Describe the solution you'd like
If I have a cover layout. How can I render a title in the template?

example.md

---
layout: cover
title: My Title
---

/layouts/cover.vue

<template>
   <div class="slidev-layout cover"
     <h1>{/* How do I render "My Title" here? */}</h1>
     <slot />
   </div>
</template>

Describe alternatives you've considered
The way I currently do it is by manually styling h1 tags inside the cover css class.

[kermanx]

Try $frontmatter.title?

Here are some docs: https://sli.dev/guide/global-context#frontmatter