Avoid forcing diagnostic message in ErrorType
Avoid forcing diagnostic message in ErrorType

I found the problem when trying to debug what went wrong with encoded names
in backend. I added an assert that the toString of a name would not contain
symbolic operator characters. The assert triggered because an error type forced
the message (without printing to Console later).

som-snytt/dotty,dotty-staging/dotty,som-snytt/dotty,som-snytt/dotty,lampepfl/dotty,lampepfl/dotty,dotty-staging/dotty,dotty-staging/dotty,lampepfl/dotty,sjrd/dotty,dotty-staging/dotty,sjrd/dotty,dotty-staging/dotty,som-snytt/dotty,lampepfl/dotty,sjrd/dotty,lampepfl/dotty,sjrd/dotty,som-snytt/dotty,sjrd/dotty