Feature: Add linebreaks to error message

See screenshot:

It's extremely hard to find out, which NonNull is causing the error/warning. Could you please add a line break right before inserting the type definition, so they both begin on a new line like this:
```
Null type safety (type annotations): The expression of type
'@NonNull Comparator>>' needs unchecked conversion to conform to
'@NonNull Comparator>>'
```
As a bonus feel free to add any whitespace alignment, highlighting or other comparison helper ...

No file, test, or entry point is named in the issue. Start by locating the diagnostic text for the null type safety message in the Java compiler sources and its existing tests; done means the type definition begins on a new line and the diagnostic tests pass with the updated wording.

Written by the indexing model from the issue text.