Faster Null Path Selection in ArrayData Equality

[dhruv9vats]

Which issue does this PR close?

Closes #2188.

Rationale for this change

What changes are included in this PR?

For the operations that only need to know if there are any nulls to select a more optimized code path, we instead of counting nulls in both lhs and rhs null masks:

• Replace count_nulls with contains_nulls to not have to traverse the whole bitmap once a null is found.
• Only check for nulls in lhs ArrayData's null mask, as at these points in execution, the null masks have already been compared.

Are there any user-facing changes?

No.

[tustvold]

LGTM, I think a comment explaining that the null masks have already been checked would be a good addition

[dhruv9vats]

Skipping this one as we do use the null_count here:

arrow-rs/arrow/src/array/equal/list.rs

Lines 94 to 101 in c8bf1ca

	let lhs_null_count = count_nulls(lhs.null_buffer(), lhs_start + lhs.offset(), len);
	let rhs_null_count = count_nulls(rhs.null_buffer(), rhs_start + rhs.offset(), len);
	if lhs_null_count != rhs_null_count {
	return false;
	}
	if lhs_null_count == 0 && rhs_null_count == 0 {

[ursabot]

Benchmark runs are scheduled for baseline = b36bc88 and contender = c25d16e. c25d16e is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-rs-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java