refactor: rename _ex() -> _ext()

"ex" means "used to be, but no longer is".
"ext" means "extended", which is the intended meaning.
"Ext" is more common not only in the Rust ecosystem but in general.
We already had several people (myself included) asking
what "ex" is supposed to mean.

To reproduce this commit, search and replace `_ex(?!\w)` -> `_ext`.
But don't change `list_transports_ex` because it's public API.

deltachat-ffi/src/lib.rs

@@ -1065,7 +1065,7 @@ pub unsafe extern "C" fn dc_send_delete_request(
     let ctx = unsafe { &*context };
     let msg_ids = convert_and_prune_message_ids(msg_ids, msg_cnt);
 
-    block_on(message::delete_msgs_ex(ctx, &msg_ids, true))
+    block_on(message::delete_msgs_ext(ctx, &msg_ids, true))
         .context("failed dc_send_delete_request() call")
         .log_err(ctx)
         .ok();
@@ -1308,7 +1308,7 @@ pub unsafe extern "C" fn dc_get_chat_msgs(
 
     let add_daymarker = (flags & DC_GCM_ADDDAYMARKER) != 0;
     Box::into_raw(Box::new(
-        block_on(chat::get_chat_msgs_ex(
+        block_on(chat::get_chat_msgs_ext(
             ctx,
             ChatId::new(chat_id),
             MessageListOptions { add_daymarker },