Enable paginators when code generating with the orchestrator (#2688)

## Motivation and Context
The paginators were originally turned off for the orchestrator feature
flag since there were issues with them, but those issues seem to have
been resolved since. This PR re-enables them.

## Testing
- [x] Generated the AWS SDK in `orchestrator` mode and verified the
paginator tests pass
- [x] Added a unit test that validates the paginators compile for
generic clients in `orchestrator` mode

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