Recognise wrong QR code type in every scanner

When a scanner is shown a QR code of a different kind than it expects, it
now tells the user what they actually scanned and where to use it, instead
of a generic "invalid" message.

Link recognition is done in the core: a new chat_check_link export
classifies a scanned string using the same decoders the views use to
process the links (connection link, server address, migration file link,
desktop address, security code), returning a typed result. Each scanner
calls checkLink first; the expected type proceeds to that scanner's normal
success path, a recognised-but-wrong type shows a shared wrong-type alert
saying what it is and where to use it, and an unrecognised string falls
back to that scanner's own contextual error. Mirrored on Android, desktop
and iOS.

Note: the iOS Swift was written without an Xcode toolchain and is not yet
compiled — needs a Mac/CI build to verify.

libsimplex.dll.def

@@ -12,6 +12,7 @@ EXPORTS
     chat_recv_msg_wait
     chat_parse_markdown
     chat_parse_server
+    chat_check_link
     chat_parse_uri
     chat_password_hash
     chat_valid_name