[Feature request] Add option to annotate using next button

[halidaee]

It would be great to add an option so that an end user could have annotations added as a 'next slide', transitioning in similarly to fragments, instead of needing to press 'R'. This is especially useful in contexts where a presentation remote is being used. Not sure if this is possible given Quarto's extension format, however.

[mirenbz]

This, and the lack of an option to "unshow" / hide annotations (that I've found, at least), is keeping me using fragments to add highlights. Any chance of progress in this? Thanks!