arrow

GH-35573: [Python] pa.FixedShapeTensorArray.to_numpy_ndarray fails on sliced arrays (#36164)

### Rationale for this change
`pa.FixedShapeTensorArray.to_numpy_ndarray` fails if called on a sliced `FixedShapeTensorArray`.

### What changes are included in this PR?
The use of `pyarrow.FixedSizeListArray.values` is replaced with `pyarrow.FixedSizeListArray.flatten()` in `FixedShapeTensorArray.to_numpy_ndarray`.

### Are these changes tested?
Yes, test is added to _python/pyarrow/tests/test_extension_type.py_

### Are there any user-facing changes?
No.
* Closes: #35573

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