When a key is gossiped for the contact in a verified chat,
it is stored in the secondary verified key slot.
The messages are then encrypted to the secondary verified key
if they are also encrypted to the contact introducing this secondary key.
Chat-Group-Member-Added no longer updates the verified key.
Verified group recovery only relies on the secondary verified key.
When a message is received from a contact
signed with a secondary verified key,
secondary verified key replaces the primary verified key.
When verified key is changed for the contact
in response to receiving a message
signed with a secondary verified key,
"Setup changed" message is added
to the same chat where the message is received.
this pr keeps and refines documentation added in #4951, however, reverts
the api introduced by #4951
which turns out to be not useful for UI in practise:
UI anyway check for chat/no-chat beforehand,
so a simple condition in profiles as
`green_checkmark = chat_exist ? chat_is_protected() :
contact_is_verified()`
is more useful in practise and is waht UI need and did already in the
past. (https://github.com/deltachat/deltachat-android/pull/2836 shows a
detailed discussion)
(as a side effect, beside saving code,
this PR saves up to three database calls
(get contact from chat in UI to pass it to profile_is_verified(), get
chat from contact in core, load is_protected in core) - instead, core
can use already is_protected from already loaded chat object)
/me did check rust-tests, fingers crossed for python tests
/me should re-setup python tests on local machine at some point :)
