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GH-38553 : [C++] Replace null_count with MayHaveNulls in ListArrayFromArray and MapArray (#41957)

### Rationale for this change

Offsets could have `null_count() == -1` (`kUnknownNullCount`) meaning that offsets might contain nulls that are not accounted for which can produce failures (https://github.com/apache/arrow/issues/38553) when working with `ListArray` or `MapArray`. `null_count()` should be replaced with `MayHaveNulls()`.

### What changes are included in this PR?

`null_count` is replaced with `MayHaveNulls` in `ListArrayFromArray`,  `MapArray::FromArraysInternal` and `MapArray::ValidateChildData`. Some tests had to be updated.

### Are these changes tested?

Yes.

### Are there any user-facing changes?

No.
* GitHub Issue: #38553

Authored-by: AlenkaF <frim.alenka@gmail.com>
Signed-off-by: Felipe Oliveira Carvalho <felipekde@gmail.com>