arrow

GH-40062: [C++] Move RecordBatch::ToTensor code from record_batch.cc to tensor.cc (#41932)

### Rationale for this change

This is a precursor PR to https://github.com/apache/arrow/pull/41870 with the purpose to make the review of #41870 easier (the diff of the code will be visible as it currently isn't because the code was moved to table.cc. I should also live in tensor.cc).

### What changes are included in this PR?

The code from `RecordBatch::ToTensor` in record_batch.cc is moved to `RecordBatchToTensor` in tensor.cc.

### Are these changes tested?

Existing tests should pass.

### Are there any user-facing changes?

No.

**This PR does not close the linked issue yet, it is just a precursor!**
* GitHub Issue: #40062

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