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GH-41684: [C++][Python] Add optional null_bitmap to MapArray::FromArrays (#41757)

### Rationale for this change

When constructing a `MapArray` with `FromArrays` one can not supply a `null_bitmap`.

### What changes are included in this PR?

Optional `null_bitmap` argument is added to `MapArray::FromArrays`.

### Are these changes tested?

TODO (have them locally, need to clean them up and commit.

### Are there any user-facing changes?

No.
* GitHub Issue: #41684

Authored-by: AlenkaF <frim.alenka@gmail.com>
Signed-off-by: Joris Van den Bossche <jorisvandenbossche@gmail.com>