Add layout = auto

[cscheid]

Will close #7832.

• Requires Pandoc dependency refresh for pandoc.image API.
• Currently only works on LaTeX because of layout algorithm mismatch between LaTeX and HTML

Usage

layout attribute now supports auto keyword, which we take to mean "layout all cells in a single row and automatically adjust image heights so they're all matched."

Example:

---
title: hello
---

::: {#fig-1 layout=auto} 

![Hanno](./hanno.png)

![Surus](./surus.png)

Elephants

:::

See @fig-1

LaTeX output

HTML output

Currently broken: