Determine if a subtree has any directory object changes and if it
doesn't skip traversing that subtree during hierarchy merging.
"Directory object changes" for a subtree are defined as:
* moving/renaming a directory within the subtree
* deleting a directory in the subtree
* moving a directory into the subtree
* creating a directory in the subtree
* moving a directory out of the subtree
The resulting snapshot still contains all data in the
pruned subtree.
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#### Does this PR need a docs update or release note?
- [x] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [ ] ⛔ No
#### Type of change
- [x] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Supportability/Tests
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup
#### Issue(s)
* #4117
#### Test Plan
- [ ] 💪 Manual
- [x] ⚡ Unit test
- [x] 💚 E2E
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