Errors and warnings hard to distinguish in the repl

[lrytz]

It's not easy to see if a message was a warning or an error. The only difference is the missing result line.

[newca12]

This is what we see with Dotty 0.14.0-RC1 but with Dotty HEAD the line number does have a distinct color to distinguish errors and warnings.

[smarter]

Yes, see #6293, so closing this, but feel free to discuss other improvements on https://contributors.scala-lang.org/ for example.