GSProcessing mask and label output can be mis-ordered

[thvasilo]

We've observed mis-orderings between masks and label values when labels are transformed with GSProcessing. So far we've only observed in node classification cases, where the labels contain missing values, but we need to verify order for all types of labels.

• Fix label/mask order mismatch for node classification. #1138
• Fix label/mask order mismatch for edge classification. #1139
• Verify label/mask order matching for node regression.
• Verify label/mask order matching for edge regression.
• Verify label/mask order matching for link prediction.