For contiguous inputs, bump local-work-group size from 64 to 128 work-items.

This change is guided by performance study on Newton root finding example rich in elementwise operations.

With this change, unitrace states that 311 invocations of the kernel took 2805824666 ns, before that, with 64 workitems, the time was 3475091844 ns.

                                                      "dpctl::tensor::kernels::multiply::multiply_inplace_contig_kernel<std::complex<float>, std::complex<float>, 4u, 2u>[SIM
D16 {15625; 1; 1} {128; 1; 1}]",          311,           2805824666,    25.380501,              9021944,              8915416,              9143437                          

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