Makes modifications to the groups handlers to facilitate the incoming introduction of conversations backup handling. Changes include:
* new handler methods (canMakeDeltas and LocationRef)
* binding handlers to generics
* some naming normalization
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#### Does this PR need a docs update or release note?
- [x] ⛔ No
#### Type of change
- [x] 🌻 Feature
#### Issue(s)
* #4536
#### Test Plan
- [x] ⚡ Unit test
- [x] 💚 E2E