Allow replying to multiple messages at once

[Septicity]

Current problem

Sometimes, in specific contexts, multiple people say something that I will have the same response to. My only options are to reply multiple times or reply to one message, then "CC" others by pinging them.

Proposed change

Being able to reply to multiple messages at once, such that the reply ping goes to everyone involved, would help with this.

Additional information

Stoat's implementation, in my experience, is a good reference.

Acknowledgements

• I searched existing discussions.

[VAdaPEGA]

Leaving screenshots from Stoat's multi-quote feature here for those curious to see what it looks like but have no interest in checking it for themselves.

It allows to selectively ping each individual user.

[Arkatneil]

This could be a good addition to the proposals outlined in the neighboring idea https://github.com/orgs/fluxerapp/discussions/1162. To be able to reply at multiple messages at once, first of all we need ability to select multiple messages..