Providing api for getting to know if a keyword is a preprocessor keyword or not in Index.h

Hi.

I found no api in Index.h to find if a keyword is preprocessor keyword or not, so had to use some other header file like TokenKinds.h and make my own implementation for finding that.
Can someone please tell is there any specific reason not to provide the api and can I contribute my implementation by providing the api for the same in index.h .

Regards,
Himanshu Mishra