[PyTorch] Make RecordFunction::active private (#47549)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47549
In preparation for moving state onto the heap.
ghstack-source-id: 117027862
Test Plan: CI
Reviewed By: ilia-cher
Differential Revision: D24812214
fbshipit-source-id: 1455c2782b66f6a59c4d45ba58e1c4c92402a323
