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ARROW-13893: [R] Make head/tail lazy on datasets and queries

Additional changes included here:

* `collapse()` now correctly propagates `group_by()` information
* `Scanner$create()` now accepts a `RecordBatchReader`
* `head`/`tail` methods added for `Scanner` and `RecordBatchReader`
* ExecPlan::StopProducing is exposed (`ExecPlan$Stop()`)

Followups:

* ARROW-14289: Refactor `Scanner::Head` to return a `RecordBatchReader` instead of a `Table` (history: #10047)
* ARROW-14288: Handle nrow with head/tail, possibly more with collapsed queries

Closes #11373 from nealrichardson/head-tail

Authored-by: Neal Richardson <neal.p.richardson@gmail.com>
Signed-off-by: Neal Richardson <neal.p.richardson@gmail.com>