feat: add MsgReadCountChanged event

Useful for updating the read count on channel messages live.

This supersedes https://github.com/chatmail/core/pull/7979.
Unlike that MR, this one is not breaking.

Needed for https://github.com/deltachat/deltachat-desktop/issues/5220.

deltachat-ffi/deltachat.h

@@ -6341,6 +6341,15 @@ void dc_event_unref(dc_event_t* event);
  */
 #define DC_EVENT_MSG_DELETED              2016
 
+/**
+ * Like @ref DC_EVENT_MSG_READ, but also fires on subsequent MDNs,
+ * if there are multiple receivers, i.e. in groups and channels.
+ *
+ * @param data1 (int) chat_id
+ * @param data2 (int) msg_id
+ */
+#define DC_EVENT_MSG_READ_COUNT_CHANGED   2018
+
 
 /**
  * Chat changed. The name or the image of a chat group was changed or members were added or removed.

deltachat-ffi/src/lib.rs

@@ -528,6 +528,7 @@ pub unsafe extern "C" fn dc_event_get_id(event: *mut dc_event_t) -> libc::c_int
         EventType::MsgFailed { .. } => 2012,
         EventType::MsgRead { .. } => 2015,
         EventType::MsgDeleted { .. } => 2016,
+        EventType::MsgReadCountChanged { .. } => 2018,
         EventType::ChatModified(_) => 2020,
         EventType::ChatEphemeralTimerModified { .. } => 2021,
         EventType::ChatDeleted { .. } => 2023,
@@ -602,6 +603,7 @@ pub unsafe extern "C" fn dc_event_get_data1_int(event: *mut dc_event_t) -> libc:
         | EventType::MsgFailed { chat_id, .. }
         | EventType::MsgRead { chat_id, .. }
         | EventType::MsgDeleted { chat_id, .. }
+        | EventType::MsgReadCountChanged { chat_id, .. }
         | EventType::ChatModified(chat_id)
         | EventType::ChatEphemeralTimerModified { chat_id, .. }
         | EventType::ChatDeleted { chat_id } => chat_id.to_u32() as libc::c_int,
@@ -688,7 +690,8 @@ pub unsafe extern "C" fn dc_event_get_data2_int(event: *mut dc_event_t) -> libc:
         | EventType::MsgDelivered { msg_id, .. }
         | EventType::MsgFailed { msg_id, .. }
         | EventType::MsgRead { msg_id, .. }
-        | EventType::MsgDeleted { msg_id, .. } => msg_id.to_u32() as libc::c_int,
+        | EventType::MsgDeleted { msg_id, .. }
+        | EventType::MsgReadCountChanged { msg_id, .. } => msg_id.to_u32() as libc::c_int,
         EventType::SecurejoinInviterProgress { progress, .. }
         | EventType::SecurejoinJoinerProgress { progress, .. } => *progress as libc::c_int,
         EventType::ChatEphemeralTimerModified { timer, .. } => timer.to_u32() as libc::c_int,
@@ -762,6 +765,7 @@ pub unsafe extern "C" fn dc_event_get_data2_str(event: *mut dc_event_t) -> *mut
         | EventType::MsgFailed { .. }
         | EventType::MsgRead { .. }
         | EventType::MsgDeleted { .. }
+        | EventType::MsgReadCountChanged { .. }
         | EventType::ChatModified(_)
         | EventType::ContactsChanged(_)
         | EventType::LocationChanged(_)