[BE] Use `std::make_unique` (#110298)
Since C++14 `std::unique_ptr<type_t[]> x(new type_t[NUM])` is identical to `auto x = std::make_unique<type_t[]>(NUM);`
Leave two `std::unique_ptr<float[]> arr(new float[NUM]());` as statement not just allocates, but initializes it as well, se e below:
https://github.com/pytorch/pytorch/blob/d04b35e7e31547c3cdb9684e1dd0b556bf593a93/aten/src/ATen/native/cpu/SoftMaxKernel.cpp#L700-L701
On the other hand, from https://github.com/pytorch/pytorch/pull/60371 it's not at all clear, if it needs to be initialized to zero at that point...
Pull Request resolved: https://github.com/pytorch/pytorch/pull/110298
Approved by: https://github.com/kit1980
