Alt tag is wrong when using html captions

[zackdotcomputer]

Steps to reproduce the behavior: Use the feature supporting html string captions

Expected behavior: The alt tag should either be the string-only contents of the html caption or should be settable via an additional props value.

Actual behavior: The alt tag is the raw HTML markup and there is no way to fix or override.

[zackdotcomputer]

Ooooh I'm trying to fix this - is the way to do this to override the Formatters? I might still open a PR to add this as a supported prop.