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

compiler/rustc_errors/src/lib.rs

@@ -573,6 +573,7 @@ impl Handler {
             None,
             flags.macro_backtrace,
             flags.track_diagnostics,
+            TerminalUrl::No,
         ));
         Self::with_emitter_and_flags(emitter, flags)
     }
@@ -1838,6 +1839,13 @@ pub fn add_elided_lifetime_in_path_suggestion(
     );
 }
 
+#[derive(Clone, Copy, PartialEq, Hash, Debug)]
+pub enum TerminalUrl {
+    No,
+    Yes,
+    Auto,
+}
+
 /// Useful type to use with `Result<>` indicate that an error has already
 /// been reported to the user, so no need to continue checking.
 #[derive(Clone, Copy, Debug, Encodable, Decodable, Hash, PartialEq, Eq, PartialOrd, Ord)]