keep extra_info of each op in ProfDagStats (#15244)

keep extra_info of each op in ProfDagStats (#15244)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15244

This DIFF keeps track of the extra_info information attached to each operator. When getPerOpStas() is called, it attaches the extra_info to the result ProfDagStats protobuf.

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Net transform attaches a global_op_id which is defined as a tuple of (orig_net_name, original_op_index) to each operator,
The global_op_id is encoded as extra_info in each operator.

Reviewed By: aazzolini

Differential Revision: D13016289

fbshipit-source-id: 3e2719ec7ed0ebe47740b77581c565ff7e79b102