slightly nicer and shorter QR and invite codes (#7390)

- sort garbage to the beginning, readable text to the end
- instead of `%20`, make use of `+` to encode spaces
- shorter invite links and smaller QR codes by truncation of the names

the truncation of the name uses chars() which does not respect grapheme clusters, so
that last character may be wrong. not sure if there is a nice and easy
alternative, but maybe it's good engoug - the real, full name will come
over the wire (exiting truncate() truncates on word boundaries, which is
maybe too soft here - names may be long, depending on the language, and
not contain any space)

moreover, this resolves the "name too long" issue from
https://github.com/chatmail/core/issues/7015

---------

Co-authored-by: Hocuri <hocuri@gmx.de>

src/securejoin/securejoin_tests.rs

@@ -1070,3 +1070,46 @@ async fn test_rejoin_group() -> Result<()> {
 
     Ok(())
 }
+
+/// To make invite links a little bit nicer, we put the readable part at the end and encode spaces by `+` instead of `%20`.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_get_securejoin_qr_name_is_last() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    alice
+        .set_config(Config::Displayname, Some("Alice Axe"))
+        .await?;
+    let qr = get_securejoin_qr(alice, None).await?;
+    assert!(qr.ends_with("Alice+Axe"));
+
+    let alice_chat_id = chat::create_group(alice, "The Chat").await?;
+    let qr = get_securejoin_qr(alice, Some(alice_chat_id)).await?;
+    assert!(qr.ends_with("The+Chat"));
+
+    Ok(())
+}
+
+/// QR codes should not get arbitrary big because of long names.
+/// The truncation, however, should not let the url end with a `.`, which is a call for trouble in linkfiers.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_get_securejoin_qr_name_is_truncated() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    alice
+        .set_config(
+            Config::Displayname,
+            Some("Alice Axe Has A Very Long Family Name Really Indeed"),
+        )
+        .await?;
+    let qr = get_securejoin_qr(alice, None).await?;
+    assert!(qr.ends_with("Alice+Axe+Has+A+Very+Lon_"));
+    assert!(!qr.ends_with("."));
+
+    let alice_chat_id =
+        chat::create_group(alice, "The Chat With One Of The Longest Titles Around").await?;
+    let qr = get_securejoin_qr(alice, Some(alice_chat_id)).await?;
+    assert!(qr.ends_with("The+Chat+With+One+Of+The_"));
+    assert!(!qr.ends_with("."));
+
+    Ok(())
+}