Templatize Tensor.data_ptr() (#24847)
Summary:
This PR templatizes `Tensor.data_ptr()`, to prepare for the deprecation of `Tensor.data<T>()` and introduction of `Tensor.data()` that has the same semantics as `Variable.data()`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24847
Differential Revision: D16906061
Pulled By: yf225
fbshipit-source-id: 8f9db9fd105b146598a9d759aa4b4332011da8ea
