feat: Remove webxdc info messages together with webxdc

[Septias]

This PR adds the feature that webxdc info messages belonging to a wexbdc are deleted when the webxdc is deleted. This is implemented by checking every deleted message whether it has referencing messages with the SystemMessage WebxdcInfoMsg. These messages are then deleted locally, and a delete request is sent out to chat peers. Deletion could also be implemented on the receiving side of a webxdc delete, but with the current implementation, the code is nice and concise and in one place.

close #6999

[Hocuri]

Did you test whether this actually works on a real device (DC Android/Desktop)?

Because @adbenitez commented:

they have different IDs per device so deleting in one device doesn't delete for everyone nor even for your oder devices, so you have to delete several info message manually from every device

[Septias]

No, I have to test it on a real device. But rfc724 mid should be be the same across devices, no?

[r10s]

No, I have to test it on a real device.

that should be done, building desktop is comparable easy - and testing multi device should be possible by ex-/importing a backup

But rfc724 mid should be be the same across devices, no?

no. seems they're generated locally and are different on devices. at least this is what i read from the webxdc.rs code at a first glance, reading for 30 seconds :)

not saying the PR is not working, however, only answering the question :) as said, testing makes sense here