Allow captioning uploads

[matrixbot]

Created by @ Amandine:matrix.org.

from Shrike: I find myself wanting to upload a photo with a message quite often (or any file really)

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[turt2live]

This could be achieved by (ab)using the new functionality in Riot where images can now be in the message body. Could also have the RTE work gmail-style where the image is dumped in the content view and you're able to edit the text around it.

[richvdh]

related doc issue: https://github.com/matrix-org/matrix-doc/issues/906

[turt2live]

ux-wise, hipchat isn't horrible for this:

although in practice this issue is dealt with by element-hq/element-web#7565

[MurzNN]

Good UI for attaching images and files to message have vk.com/im messenger service. Best is to have them inline into message edit area, but this is too hard to implement. So, at first, will be great to see them as separate attachments panel near to edit box.

[bbigras]

This feature would be very useful. I almost always want to send text explaining the image upload. Having only 1 message would be cleaner and would only notify people once.

Discord is handling this very well too:

[Biep]

If threading (#2349) is done really well (as in fully modular), it should not only allow higher units such as communities, but also lower units, including combinations of messages from the same sender, of which image + caption would be one instance.
(And of course it could implement reactions and edits too, unifying the code.)

[bbigras]

If threading (#2349) is done really well (as in fully modular), it should not only allow higher units such as communities, but also lower units, including combinations of messages from the same sender, of which image + caption would be one instance.

If you have notifications ON, would you get one or two notifications for a image + caption message?

[chutten]

I would consider this an accessibility feature. Screen-reader users might benefit from captions describing an otherwise-opaque upload (like an image). The UI could be helpful by explaining how to write good captions and how they're useful.