Is your feature request related to a problem? Please describe.

The $slidev.frontmatter is not set in a global-top, or global-bottom. Instead we are pointed to the $nav to obtain information about the current slide. However, that does give us access to the currentLayout which is useful, but I'd have liked to have more general access to other fields in the frontmatter of the current slide.

Describe the solution you'd like
Exposure nav.currentFrontmatter

Describe alternatives you've considered
Make $slidev.frontmatter be populated for a global-top.vue or global-bottom.vue.