Qualcomm AI Engine Direct - increase index_put coverage (#14924)

### Summary
- refactor a bit & add more test cases


### Test plan
```bash
python backends/qualcomm/tests/test_qnn_delegate.py TestQNNQuantizedOperator.test_qnn_backend_index_put -b build-android -s $SN -m SM8750
python backends/qualcomm/tests/test_qnn_delegate.py TestQNNQuantizedOperator.test_qnn_backend_index_put_suite -b build-android -s $SN -m SM8750
```

Author: haowhsu-quic