Handle inline images better when hiding images

(I'm failing to find the right title phrasing here, so update if you have a better one)

I have showImages turned off on my account, which causes inline images to be discarded (expected). However this means that if someone sends me a message with an inline image that conveys a meaning, all context is lost there. I'd probably expect to see the use of the `alt` tag in it's place at a minimum, just so the context isn't lost.

Related (and would probably help my issue https://github.com/vector-im/element-meta/issues/1662)