arrow

GH-40750: [C++][Python] Map child Array constructed from keys and items shouldn't have offset (#40871)

### Rationale for this change

When `MapArray` is constructed from `keys` and `items` array the offset of the list offsets is passed down to the struct child array which is not correct.

### What changes are included in this PR?

This PR fixes this issue.

### Are these changes tested?

Yes.

### Are there any user-facing changes?

Shouldn't be.
* GitHub Issue: #40750

Authored-by: AlenkaF <frim.alenka@gmail.com>
Signed-off-by: AlenkaF <frim.alenka@gmail.com>