*   Add templates and interfaces for creating lookup tables
    *   `Tensor::UnsafeCopyFromInternal` deprecated in favor
        `Tensor::BitcastFrom`.
    *   In `map_vectorization` optimization, reduce the degree of parallelism in
        the vectorized map node.
    *   Add variant wrapper for `absl::string_view`.
    *   Add OpKernels for some stateless maps.