Syntax highlighter wont recognize nested comments

[joseluis]

Dart has nested comments, but the syntax highlighter doesn't recognize them. For example:

/*
/*
 Comment

 /* nested comment */
​
*/ // <-- not highlighted
​
main() {}

Downstream: https://github.com/github/linguist/issues/2872 Related: https://github.com/dart-lang/sdk/issues/25931