[c10d] switch ProcessGroup to be managed by intrusive_ptr (#47343)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/47343
Test Plan: Imported from OSS
Reviewed By: gmagogsfm
Differential Revision: D24723418
Pulled By: wanchaol
fbshipit-source-id: 0463819b96c53b12bdbb3905431110d7b21beb77
