add partition_by_partition_cost (#47280)
Summary:
This PR adds the support to calculate the cost of a partitioned graph partition by partition based on the node cost. In a partitioned graph, top partitions (partitions without parents) are collected as the starting points, then use DFS to find the critical path among all partitions in the graph
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47280
Reviewed By: gcatron
Differential Revision: D24735932
Pulled By: scottxu0730
fbshipit-source-id: 96653a8208554d2c3624e6c8718628f7c13e320b
