GH-17211: [C++] Add hash32 and hash64 scalar compute functions

[kszucs]

Rationale for this change

Support for calculating elementwise hashes.

The PR adds to scalar functions hash32() and hash64() using the existing internal hashing machinery.

What changes are included in this PR?

Continuation of #39836 with the following changes:

• Use column oriented hash-combine rather than flattening nested elements
• Support arbitrary nesting levels with an optimization that only hash child arrays if they are also nested

Are these changes tested?

Partially, working on a proper testing suite.

Are there any user-facing changes?

There is a new compute kernel hash_64 available.

• GitHub Issue: [C++][Compute] Add scalar_hash function #17211

[kszucs]

Seems like we generate the same hash for both NULL and 0 which is not ideal.

In [1]: import pyarrow as pa

In [2]: import pyarrow.compute as pc

In [3]: pc.hash_64([None])
Out[3]:
<pyarrow.lib.UInt64Array object at 0x124247be0>
[
  0
]

In [4]: pc.hash_64([0])
Out[4]:
<pyarrow.lib.UInt64Array object at 0x1033027a0>
[
  0
]

[zanmato1984]

Some first glance comments. I'll look into more details later.

[a-reich]

Just asking - any idea if there is line of sight to this issue being closed? I am interested because, among other things, I believe this Arrow functionality is the underlying reason why pandas cannot currently group by a pyarrow-backed struct series.