public void writeVocabFile() {
		// write out the vocab interchange file; used by antlr,
		// does not change per target
		ST tokenVocabSerialization = getTokenVocabOutput();
		String fileName = getVocabFileName();
		if ( fileName!=null ) {
			target.genFile(g, tokenVocabSerialization, fileName);
		}
	}
Generate a token vocab file with all the token names/types.  For example:
 ID=7
 FOR=8
 'for'=8

 This is independent of the target language; used by antlr internally
tool/src/org/antlr/v4/codegen/CodeGenerator.java