public void writeListener(ST outputFileST, SourceType sourceType) {
		target.genFile(g, outputFileST, getListenerFileName(sourceType));
	}
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