[ODRHash] Handle `Integral` and `NullPtr` template parameters in `ODRHash`

Before this patch the parameters mentioned in the title weren't
handled by ODRHash, when a hash was generated for a template
specialization. This patch adds these parameters to the hash,
so that different template specializations will get different
hashes in every case.

Differential Revision: https://reviews.llvm.org/D141224