add dc_msg_set_override_sender_name() api

with mailinglists, we already receive and handle per-message-names,
this api allows this also eg. for bots based on the deltachat api.

deltachat-ffi/deltachat.h

@@ -3816,6 +3816,21 @@ void            dc_msg_set_text               (dc_msg_t* msg, const char* text);
 void            dc_msg_set_html               (dc_msg_t* msg, const char* html);
 
 
+/**
+ * Set different sender name for a message.
+ * This overrides the name set by the dc_set_config()-option `displayname`.
+ *
+ * Usually, this function is not needed
+ * when implementing pure messaging functions.
+ * However, it might be useful for bots eg. building bridges to other networks.
+ *
+ * @memberof dc_msg_t
+ * @param msg The message object.
+ * @param name The name to send along with the message.
+ */
+void            dc_msg_set_override_sender_name(dc_msg_t* msg, const char* name);
+
+
 /**
  * Set the file associated with a message object.
  * This does not alter any information in the database

deltachat-ffi/src/lib.rs

@@ -3028,6 +3028,21 @@ pub unsafe extern "C" fn dc_msg_set_html(msg: *mut dc_msg_t, html: *const libc::
     ffi_msg.message.set_html(to_opt_string_lossy(html))
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn dc_msg_set_override_sender_name(
+    msg: *mut dc_msg_t,
+    name: *const libc::c_char,
+) {
+    if msg.is_null() {
+        eprintln!("ignoring careless call to dc_msg_set_override_sender_name()");
+        return;
+    }
+    let ffi_msg = &mut *msg;
+    ffi_msg
+        .message
+        .set_override_sender_name(to_opt_string_lossy(name))
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn dc_msg_set_file(
     msg: *mut dc_msg_t,