[Dataset] Change the Data Type of the Node Features in GINDataset/TUDataset from Float64 to Float32

[mufeili]

Description

As reported in this thread by @hengruizhang98 , the node feature attr of the graphs in GINDataset has a data type of float64 rather than float32. This PR addresses the issue in instantiating the datasets.

@BarclayII @jermainewang This is not a critical issue and we may merge it after we are done with 0.6 release.

Checklist

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [$CATEGORY] (such as [NN], [Model], [Doc], [Feature]])
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented
• To the my best knowledge, examples are either not affected by this change,
  or have been fixed to be compatible with this change
• Related issue is referred in this PR
• If the PR is for a new model/paper, I've updated the example index here.

[hetong007]

Should we apply this as a standard practice to other graph classification datasets (e.g. TU)?

Currently in the example, we have lines converting the dtype:

https://github.com/dmlc/dgl/blob/master/examples/pytorch/gin/main.py#L25-L26
https://github.com/dmlc/dgl/blob/master/examples/pytorch/sagpool/main.py#L85-L86
https://github.com/dmlc/dgl/blob/master/examples/pytorch/hgp_sl/main.py#L93-L94

[mufeili]

Should we apply this as a standard practice to other graph classification datasets (e.g. TU)?

Currently in the example, we have lines converting the dtype:

https://github.com/dmlc/dgl/blob/master/examples/pytorch/gin/main.py#L25-L26
https://github.com/dmlc/dgl/blob/master/examples/pytorch/sagpool/main.py#L85-L86
https://github.com/dmlc/dgl/blob/master/examples/pytorch/hgp_sl/main.py#L93-L94

Good point. Updated.

[hetong007]

Sorry I just found these two files have the same lines, could you please clean them up together?

https://github.com/dmlc/dgl/blob/master/examples/pytorch/gxn/main.py
https://github.com/dmlc/dgl/blob/master/examples/pytorch/gxn/main_early_stop.py

Otherwise LGTM, thanks!

[mufeili]

Sorry I just found these two files have the same lines, could you please clean them up together?

https://github.com/dmlc/dgl/blob/master/examples/pytorch/gxn/main.py
https://github.com/dmlc/dgl/blob/master/examples/pytorch/gxn/main_early_stop.py

Otherwise LGTM, thanks!

Done.