Rollup merge of #59128 - oli-obk:colorful_json, r=mark-i-m,eddyb

Emit ansi color codes in the `rendered` field of json diagnostics

cc @ljedrz

Implemented for https://github.com/rust-lang/rust/pull/56595#issuecomment-447645115 (x.py clippy)

src/libsyntax/parse/lexer/mod.rs

@@ -1920,6 +1920,7 @@ mod tests {
         let emitter = errors::emitter::EmitterWriter::new(Box::new(io::sink()),
                                                           Some(sm.clone()),
                                                           false,
+                                                          false,
                                                           false);
         ParseSess {
             span_diagnostic: errors::Handler::with_emitter(true, None, Box::new(emitter)),