Move framework/detail/tensor-inl.h to framework/tensor-impl.h

[wangkuiyi]

Google C++ Style Guide https://google.github.io/styleguide/cppguide.html#Namespace_Names requires that the C++ namespace hierarchy matches the directory hierarchy.

Given that contents in tensor-inl.h have to be in namespace paddle::framework, we'd move the file up one level to framework directory.