arrow

GH-34519: [C++][R] Fix dataset scans that project the same name as a field (#34576)

### Rationale for this change

Fixes #34519. #33770 introduced the bug; I had [asked](https://github.com/apache/arrow/pull/33770/files#r1081612013) in the review why the C++ function wasn't using `FieldsInExpression`. I swapped that in, and the test I added to reproduce the bug now passes.

### What changes are included in this PR?

Fix for the C++ function, test in R. 

### Are these changes tested?

Yes

### Are there any user-facing changes?

The behavior observed in the report no longer happens.
* Closes: #34519

Authored-by: Neal Richardson <neal.p.richardson@gmail.com>
Signed-off-by: Weston Pace <weston.pace@gmail.com>