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.

src/securejoin.rs

@@ -481,7 +481,7 @@ pub(crate) async fn handle_securejoin_handshake(
 
             let from_addr = ContactAddress::new(&mime_message.from.addr)?;
             let autocrypt_fingerprint = mime_message.autocrypt_fingerprint.as_deref().unwrap_or("");
-            let (autocrypt_contact_id, _) = Contact::add_or_lookup_ex(
+            let (autocrypt_contact_id, _) = Contact::add_or_lookup_ext(
                 context,
                 "",
                 &from_addr,
@@ -533,7 +533,7 @@ pub(crate) async fn handle_securejoin_handshake(
                 warn!(context, "Secure-join denied (bad auth).");
                 return Ok(HandshakeMessage::Ignore);
             }
-            if Contact::lookup_id_by_addr_ex(
+            if Contact::lookup_id_by_addr_ext(
                 context,
                 &mime_message.from.addr,
                 Origin::Unknown,
@@ -663,7 +663,7 @@ pub(crate) async fn handle_securejoin_handshake(
                 ChatId::create_for_contact(context, contact_id).await?;
             }
             if let Some(joining_chat_id) = joining_chat_id {
-                chat::add_contact_to_chat_ex(context, Nosync, joining_chat_id, contact_id, true)
+                chat::add_contact_to_chat_ext(context, Nosync, joining_chat_id, contact_id, true)
                     .await?;
 
                 let chat = Chat::load_from_db(context, joining_chat_id).await?;