docs: contact profile view should not use dc_contact_is_verified()

Green checkmark in the contact profile
should only be displayed in the title
if the same checkmark is displayed in the title of 1:1 chat.
If 1:1 chat does not exist,
the checkmark should not be displayed in the title
of the contact profile.

Also add docs to is_protected
property of FullChat and BasicChat JSON objects.

src/chat.rs

@@ -1584,6 +1584,15 @@ impl Chat {
     }
 
     /// Returns true if chat protection is enabled.
+    ///
+    /// UI should display a green checkmark
+    /// in the chat title,
+    /// in the chat profile title and
+    /// in the chatlist item
+    /// if chat protection is enabled.
+    /// UI should also display a green checkmark
+    /// in the contact profile
+    /// if 1:1 chat with this contact exists and is protected.
     pub fn is_protected(&self) -> bool {
         self.protected == ProtectionStatus::Protected
     }