pandas .loc should accept an Index as the argument

The following works:
```python
import pandas as pd

df = pd.DataFrame({"x": [1, 2, 3]}, index=pd.Index(["a", "b", "c"]))

index = pd.Index(["b"])

df2 = df.loc[index]

print(df2)
```
but pylance 2021.5.3 reports for the line with the `.loc`:
```
No overloads for "__getitem__" match the provided arguments
  Argument types: (Index[str])
```

PR to follow