[CSharp] Member GetMaxTokenType missing in IVocabulary

[Martin521]

I am new to ANTLR and fascinated. I just came across the issue mentioned in the title. The GetMaxTokenType public menber is missing in the IVocabulary interface of the CSharp runtime. It is present in Vocabulary and also in the Java runtime IVocabulary. Please let me know if there is a reason for its absence.
I can create a PR if that is welcome.

• I have reproduced my issue using the latest version of ANTLR
• I have asked at stackoverflow
• Responses from the above seem to indicate that my issue could be an ANTLR bug
• I have done a search of the existing issues to make sure I'm not sending in a duplicate