Access Transformation: Add support for multi-dimensional tensors

Our current implementation only supports secret-index reads/writes for single dimensional tensor. We need to add support for multi-dimensional tensor read/write operations at:
1) Secret indices where accesses at each dimension should be transformed, and
2) Mixed secret-and-public indices where only secret-index accesses at respective dimensions should be transformed.

This transformation is part of the data-oblivious transformation pipeline (#777).