Fix DefaultDropHandler.TestCompatibleTypes for any IEditableCollectionView

[dauthleikr]

In the DefaultDropHandler:
TestCompatibleTypes does not consider any IEditableCollectionView:

...
else
{
    return target is IList;
}

This causes CanAcceptData to always reject any targets that are IEditableCollectionView, however Drop is able to handle them.

I simply modified it to:

return target is IList || target is IEditableCollectionView;

I also added some minor cleanups for the same function.

[punker76]

@dauthleikr your changes have been merged, thanks for your contribution 👍