Callout improvements for revealjs

[garthtarr]

I love the callouts but I've encountered a couple of issues using them with revealjs presentations:

• For the "simple" appearance there's an icon rendering issue (wrong size)
• The collapsible option doesn't work
• This is a little niche but it would be nice to be able to have a title only callout box, particularly for presentations. There's some distracting white space even when the content is empty. A version of the collapsible option (without the drop down arrow) would be great.

---
title: "Presentation"
format: revealjs
---

## Slide with callout

::: {.callout-note appearance="simple"}

## Simple appearance incorrect icon sizing.

Icon size incorrect.

:::

:::{.callout-caution collapse="true"}
## With option `collapse="true"` (but not collapsible)

This is an example of a 'folded' caution callout that can be expanded by the user. 
You can use `collapse="true"` to collapse it by default or `collapse="false"` to 
make a collapsible callout that is expanded by default.
:::

:::{.callout-note}

## Title only (note the unecessary white space)

:::

[jjallaire]

Hi there, thanks for the feedback! We were able to fix the 1st and 3rd issues here: 8f14b22

In terms of collapse/expand, that is currently a Bootstrap only feature.

[garthtarr]

Outstanding, thanks so much for the super quick fix - tested on the dev version and working perfectly.

[mcanouil]

FYI, "collapsible callout in Reveal.js" is tracked in #1328.