[Issue 18879] !is doesn't highlight correctly

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18879

--- Comment #1 from Rainer Schuetze <r.sagitario at gmx.de> ---
`in` and `is` can be both operators or keywords depending on context, so
different colors are expected. A preceding `!` is a separate token, i.e. there
can be arbitrary spaces and comments in between.

This makes it pretty difficult for the lexer to highlight these correctly, but
there is actually support for that by asking the parser. It seems this is
broken, though.

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