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GH-36641: [C++] Remove reference to acero from non-acero file (#36650)

### Rationale for this change

Files in modules which do not depend on the acero module should not reference files inside the acero module.

### What changes are included in this PR?

There were no changes to the body of any functions.  I simply moved functions around so that the acero include was no longer needed.  There were some conflicts that arose between the class `bit_util` and the namespace `bit_util` and so I got rid of the class in favor of the namespace as that is more similar to how we handle `bit_util` elsewhere.

### Are these changes tested?

Sort of.  I would like to add an AVX2 CI system as well.  I'm not confident any of the CI builds are building with AVX2 enabled.  Also, even if we have an AVX2 CI system it would not have caught this issue since the code was only needed definitions from the acero header and was not relying on any actual compiled symbols.  However, I think setting up tests to catch this sort of invalid include are beyond the scope of this PR.

### Are there any user-facing changes?

No.
* Closes: #36641

Lead-authored-by: Weston Pace <weston.pace@gmail.com>
Co-authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Antoine Pitrou <antoine@python.org>