[C++][Dataset] Port "head" method from R to C++ Dataset Scanner

[asfimport]

ARROW-9665 (#7913) added amongst other things a head method for Dataset in R:

arrow/r/src/dataset.cpp

Lines 266 to 282 in 586c060

	std::shared_ptr<arrow::Table> dataset___Scanner__head(
	const std::shared_ptr<ds::Scanner>& scanner, int n) {
	// TODO: make this a full Slice with offset > 0
	std::vector<std::shared_ptr<arrow::RecordBatch>> batches;
	std::shared_ptr<arrow::RecordBatch> current_batch;
	for (auto st : ValueOrStop(scanner->Scan())) {
	for (auto b : ValueOrStop(ValueOrStop(st)->Execute())) {
	current_batch = ValueOrStop(b);
	batches.push_back(current_batch->Slice(0, n));
	n -= current_batch->num_rows();
	if (n < 0) break;
	}
	if (n < 0) break;
	}
	return ValueOrStop(arrow::Table::FromRecordBatches(std::move(batches)));
	}

It might be nice to move this to C++ and expose it on the python side as well (and since it's written already in C++ on the R side, it should be relatively straightforward to port I assume)

Reporter: Joris Van den Bossche / @jorisvandenbossche
Assignee: David Li / @lidavidm

PRs and other links:

• GitHub Pull Request #10047
• GitHub Pull Request #9854

_{Note: This issue was originally created as ARROW-9731. Please see the migration documentation for further details.}

[asfimport]

Krisztian Szucs / @kszucs:
Issue resolved by pull request 10047
#10047