Introduce -Zterminal-urls to use OSC8 for error codes

Terminals supporting the OSC8 Hyperlink Extension can support inline
anchors where the text is user defineable but clicking on it opens a
browser to a specified URLs, just like `<a href="URL">` does in HTML.

https://gist.github.com/egmontkob/eb114294efbcd5adb1944c9f3cb5feda

Author: estebank

src/parse/session.rs

@@ -4,7 +4,7 @@ use std::sync::atomic::{AtomicBool, Ordering};
 use rustc_data_structures::sync::{Lrc, Send};
 use rustc_errors::emitter::{Emitter, EmitterWriter};
 use rustc_errors::translation::Translate;
-use rustc_errors::{ColorConfig, Diagnostic, Handler, Level as DiagnosticLevel};
+use rustc_errors::{ColorConfig, Diagnostic, Handler, Level as DiagnosticLevel, TerminalUrl};
 use rustc_session::parse::ParseSess as RawParseSess;
 use rustc_span::{
     source_map::{FilePathMapping, SourceMap},
@@ -135,6 +135,7 @@ fn default_handler(
             None,
             false,
             false,
+            TerminalUrl::No,
         ))
     };
     Handler::with_emitter(