Fix #2957 single quote highlighting and refactor

[maxov]

Hi all, this is my first PR so please let me know if I'm doing anything wrong.

This fixes #2957, here's a picture of how things are highlighted now:

And it does actually highlight as little as possible for characters:

I also did a tiny refactor because Chars.isLineBreakChar did the same thing as some logic in the syntax highlighter.

[felixmulder]

Hey @maxov - LGTM for the most part. Restarted the CI for your last commit.

Regarding your example with:

scala> 'a'toString

Are you writing: 'a'.toString but the highlighter is eating up the dot?

[maxov]

@felixmulder No, that is valid Scala syntax. It is postfix operator notation that also works in previous versions of scala. I use it as a test to make sure that the 'a' is not getting highlighted as two symbol literals side by side.

[felixmulder]

Unary postfix is valid, yes, we know this :)

If there are inconsistencies in the highlighting, then the most common symptom is: things get eaten up. Since we don't have tests for this - I needed to ask you.

[maxov]

I see, thanks for clarifying!