message: Fix non-deterministic order in inplace_util's IsInplaceReadOnly function
  Summary:
  Replace not_inplace_user hash set with HloIntructionSet.
  Ref T28597.
  Test Plan: All tests pass.
  Reviewers: #tensorflow, #framework_ip_review_-_any_oss_or_third-party_code_use_has_been_approved, georgep
  Maniphest Tasks: T28597
diff: @@ -263,7 +263,7 @@ bool IsInplaceReadOnly(HloInstruction* inst,
  absl::flat_hash_map<HloInstruction*, uint64> inplace_read_write_users;
  // All the non inplace uses of any cluster nodes.
  - absl::flat_hash_set<HloInstruction*> not_inplace_users;
  + HloInstructionSet not_inplace_users;
  std::queue<HloInstruction*> to_visit;
  absl::flat_hash_set<HloInstruction*> visited;
  