### What changes were proposed in this pull request?
When you use floats are index of pandas, it creates a Spark DataFrame with a wrong results as below when Arrow is enabled:
```bash
./bin/pyspark --conf spark.sql.execution.arrow.pyspark.enabled=true
```
```python
>>> import pandas as pd
>>> spark.createDataFrame(pd.DataFrame({'a': [1,2,3]}, index=[2., 3., 4.])).show()
+---+
| a|
+---+
| 1|
| 1|
| 2|
+---+
```
This is because direct slicing uses the value as index when the index contains floats:
```python
>>> pd.DataFrame({'a': [1,2,3]}, index=[2., 3., 4.])[2:]
a
2.0 1
3.0 2
4.0 3
>>> pd.DataFrame({'a': [1,2,3]}, index=[2., 3., 4.]).iloc[2:]
a
4.0 3
>>> pd.DataFrame({'a': [1,2,3]}, index=[2, 3, 4])[2:]
a
4 3
```
This PR proposes to explicitly use `iloc` to positionally slide when we create a DataFrame from a pandas DataFrame with Arrow enabled.
FWIW, I was trying to investigate why direct slicing refers the index value or the positional index sometimes but I stopped investigating further after reading this https://pandas.pydata.org/pandas-docs/stable/getting_started/10min.html#selection
> While standard Python / Numpy expressions for selecting and setting are intuitive and come in handy for interactive work, for production code, we recommend the optimized pandas data access methods, `.at`, `.iat`, `.loc` and `.iloc`.
### Why are the changes needed?
To create the correct Spark DataFrame from a pandas DataFrame without a data loss.
### Does this PR introduce _any_ user-facing change?
Yes, it is a bug fix.
```bash
./bin/pyspark --conf spark.sql.execution.arrow.pyspark.enabled=true
```
```python
import pandas as pd
spark.createDataFrame(pd.DataFrame({'a': [1,2,3]}, index=[2., 3., 4.])).show()
```
Before:
```
+---+
| a|
+---+
| 1|
| 1|
| 2|
+---+
```
After:
```
+---+
| a|
+---+
| 1|
| 2|
| 3|
+---+
```
### How was this patch tested?
Manually tested and unittest were added.
Closes#28928 from HyukjinKwon/SPARK-32098.
Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: Bryan Cutler <cutlerb@gmail.com>
1af19a7b68