[Traceable Collecive] Hide token for all_gather (#5232)
Summary:
This pull request does the following:
1. It hides token for all_gather.
2. It folds the out-of-place all_gather into the regular all_gather.
3. It fixes an issue with the last all_reduce_in_place PR where it forgot to set the token.
Test Plan:
PJRT_DEVICE=TPU python test/test_mp_all_gather.py
