[c10d] switch ProcessGroup::Work to be managed by intrusive_ptr (#44046)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/44046
Test Plan: Imported from OSS
Reviewed By: gmagogsfm
Differential Revision: D23632280
Pulled By: wanchaol
fbshipit-source-id: 0a4642a8ffabdd26c52c1baabfa30c0f446c3c85
