recognize t.me proxy qr codes (#5895)

this PR adds the type DC_QR_SOCKS5_PROXY to `dc_check_qr()` for
**supporting telegram proxy QR codes**. if returned, the UI should ask
the user if they want to us the proxy and call
`dc_set_config_from_qr();` afterwards (plus maybe `dc_configure()`).

idea is to improve our proxy story, follow ups may be:

- in UI, - move proxy out of "Account & Password", as a **separate
"Proxy Activity"** (it should stay in "Advanced" for now, however, below
"Server", which might be moved up)

- allow **opening the "Proxy Activity" from the welcome screens**
three-dot-menu (that would also solve a long standing issue that
entering the email address bypasses the proxy

- show proxy usage in the "Connectivity View" and/or add an **icon** to
the main chatlist screen (beside three-dot menu) in case some proxy is
in use; tapping this icon will open the "Proxy Activity"

- the the new "Proxy Activity", add a **share / show proxy QR code**
button. that would generate invite links in the form
`https://i.delta.chat/socks#...` - so that tapping then opens the app.
support for these links need to be added to core then.

- handle a list of proxies in core, offer selection in UI. the list
could be one for all profiles and could be filled eg. by normal invite
links or other channels

---------

Co-authored-by: iequidoo <117991069+iequidoo@users.noreply.github.com>

deltachat-ffi/src/lot.rs

@@ -52,6 +52,7 @@ impl Lot {
                 Qr::Backup { .. } => None,
                 Qr::Backup2 { .. } => None,
                 Qr::WebrtcInstance { domain, .. } => Some(domain),
+                Qr::Socks5Proxy { host, .. } => Some(host),
                 Qr::Addr { draft, .. } => draft.as_deref(),
                 Qr::Url { url } => Some(url),
                 Qr::Text { text } => Some(text),
@@ -68,7 +69,10 @@ impl Lot {
     pub fn get_text2(&self) -> Option<Cow<str>> {
         match self {
             Self::Summary(summary) => Some(summary.truncated_text(160)),
-            Self::Qr(_) => None,
+            Self::Qr(qr) => match qr {
+                Qr::Socks5Proxy { port, .. } => Some(Cow::Owned(format!("{port}"))),
+                _ => None,
+            },
             Self::Error(_) => None,
         }
     }
@@ -105,6 +109,7 @@ impl Lot {
                 Qr::Backup { .. } => LotState::QrBackup,
                 Qr::Backup2 { .. } => LotState::QrBackup2,
                 Qr::WebrtcInstance { .. } => LotState::QrWebrtcInstance,
+                Qr::Socks5Proxy { .. } => LotState::QrSocks5Proxy,
                 Qr::Addr { .. } => LotState::QrAddr,
                 Qr::Url { .. } => LotState::QrUrl,
                 Qr::Text { .. } => LotState::QrText,
@@ -131,6 +136,7 @@ impl Lot {
                 Qr::Backup { .. } => Default::default(),
                 Qr::Backup2 { .. } => Default::default(),
                 Qr::WebrtcInstance { .. } => Default::default(),
+                Qr::Socks5Proxy { .. } => Default::default(),
                 Qr::Addr { contact_id, .. } => contact_id.to_u32(),
                 Qr::Url { .. } => Default::default(),
                 Qr::Text { .. } => Default::default(),
@@ -185,6 +191,9 @@ pub enum LotState {
     /// text1=domain, text2=instance pattern
     QrWebrtcInstance = 260,
 
+    /// text1=host, text2=port
+    QrSocks5Proxy = 270,
+
     /// id=contact
     QrAddr = 320,