small cleanup in paths, primarily splitting files
so that file contents are more clearly owned, which should be a little better for readability and code placement.
Also renames `ServicePrefix` to `BuildPrefix` in
anticipation of multi-service prefixes.
no logic changes, just movement/renaming.
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#### Does this PR need a docs update or release note?
- [x] ⛔ No
#### Type of change
- [x] 🧹 Tech Debt/Cleanup
#### Issue(s)
* #3993
#### Test Plan
- [x] ⚡ Unit test
- [x] 💚 E2E