change ddpLoggingData struct to map or dict (#56641)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56641
currently ddpLoggingData is flat struct, which requires internal DDP developers and external users to know about the struct field names. This is not flexible to delete or add new fields in the future. also it is hard to access ddpLoggingData.
With maps/dict, developers and users can easily access the fields without knowing the field names, also easier to add/remove a new/old field.
Since C++ does not support map values to be different types, right now ddpLoggingData containes two types of maps.
ghstack-source-id: 127482694
Test Plan: unit tests
Reviewed By: SciPioneer
Differential Revision: D27923723
fbshipit-source-id: c90199c14925fc50ef219000e2f809dc7601cce1
