perf: Optimize array_has() for scalar needle (#20374)

## Which issue does this PR close?

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- Closes #20377.

## Rationale for this change

`compare_with_eq()` checks for matching array elements via a single pass
across the entire flat values buffer, which is reasonably fast. The
previous implementation then determined per-row results by creating a
BooleanArray slice for each row and calling `true_count()` to check for
any matches. It turns out that that's quite a lot of per-row work.

Instead, we use `BooleanBuffer::set_indices()` to iterate over the set
bits in the comparison result in a single forward pass. We walk this
iterator in lockstep with the row offsets to determine whether each row
contains a match, which does much less work per-row.

This can be substantially faster, especially for short arrays. For
example, for 10-element arrays of int64, it is 5-10x faster than the
previous approach. 10-element string arrays are 1.8-5x faster. The
improvement is smaller but non-zero for larger arrays (e.g., ~1.2x
faster for 500 element arrays).

## What changes are included in this PR?

In addition to the optimization, this commit adjusts the `array_has`
benchmark code to actually benchmark `array_has` evaluation (!). The
previous benchmark just constructed an `Expr`.

## Are these changes tested?

Yes. Passes existing tests. Performance validated via several benchmark
runs.

## Are there any user-facing changes?

No.

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Co-authored-by: Jeffrey Vo <jeffrey.vo.australia@gmail.com>

Author: neilconway