fix: Emit MsgsNoticed on receipt of an IMAP-seen message

[iequidoo]

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Let's continue the discussion here, this is a reply to https://github.com/deltachat/deltachat-core-rust/pull/6351#issuecomment-2575304115.

FTR, if we have an actual user value for emitting MsgsNoticed on receipt of an IMAP-seen message, and test that MsgsNoticed is not emitted for every reaction and mdn, then I'm not against it.

Removed emitting MsgsNoticed for the trash chat (added a check) and added such tests, though the test on receiving a seen reaction is apparently going to be broken by #6213 because reactions will be assigned to the actual chat, not to the trash. But i don't see a problem here, reactions just become hidden messages and if a reaction is seen, that's a result of an explicit user action and also means that the user has noticed notifications for earlier messages.