ashmrtn 916bb0b27c
Create an interface and implementation for Reason struct (#3868)
Intermediate step to a few different goals including
* moving interface definitions to better locations while avoid cycles
* adding a flag to disable kopia-assisted incrementals

Create an interface and implementation for the existing Reason
struct. The goal is to set stuff up so that eventually the kopia
package can ask the struct for the subtree path to work with
when merging the hierarchy instead of having the backup operation
pass that information in

Code changes are mostly just turning stuff into a struct and
fixing up compile errors. Some functions have been excluded from
the struct (i.e. `Key`) and made into functions in the kopia
package itself

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#### Does this PR need a docs update or release note?

- [ ]  Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [x]  No

#### Type of change

- [ ] 🌻 Feature
- [ ] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Supportability/Tests
- [ ] 💻 CI/Deployment
- [x] 🧹 Tech Debt/Cleanup

#### Issue(s)

* #2360

#### Test Plan

- [ ] 💪 Manual
- [x]  Unit test
- [x] 💚 E2E
2023-07-21 21:05:38 +00:00
..
2023-06-29 05:30:15 +00:00