Adding Dense Interface

[amitsingh19975]

Dense Tensors store values in a contiguous sequential block of
memory where all values are represented because of which they
heavy on memory side. If we have large amount of non-zeroes or
non-zero elements are much greater than number of zero
elements, it is prefered to store in dense as there is no gain in
using other storage type. As they are contiguous memory which
can be cached and making operations faster than other
containers.

dense_storage a empty struct which inherits from another empty base struct tensor_storage