Fix bytes_written and bytes_read (#64040)

Fix bytes_written and bytes_read (#64040)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64040

In operator cost inference functions, in many places we are using sizeof(x.data_type()). Since data_type() returns a 32 bit integer from [this enum](https://www.internalfb.com/code/fbsource/[15e7ffe4073cf08c61077c7c24a4839504b964a2]/fbcode/caffe2/caffe2/proto/caffe2.proto?lines=20), we are basically always getting 4 for sizeof(x.data_type()) no matter what actual data type x has. Big thanks to Jack Langman for specifically pointing to this bug.

We would instead use the size in bytes based on actual data type.

Test Plan:
Added unit tests BatchMatMulMemCostTest:

buck test //caffe2/caffe2/fb/fbgemm:batch_matmul_op_test -- BatchMatMulMemCostTest

Extended existing unit test test_columnwise_concat for different data types:

buck test //caffe2/caffe2/python/operator_test:concat_op_cost_test -- test_columnwise_concat

Differential Revision: D30561459

fbshipit-source-id: 976fa5167097a35af548498480001aafd7851d93