[Example] Label Propagation and Correct&Smooth

[xnuohz]

Description

Combining Label Propagation and Simple Models Out-performs Graph Neural Networks
Learning from Labeled and Unlabeled Data with Label Propagation
@mufeili

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.

Changes

[dgl-bot]

To trigger regression tests:

• @dgl-bot run [instance-type] [which tests] [compare-with-branch];
  For example: @dgl-bot run g4dn.4xlarge all dmlc/master or @dgl-bot run c5.9xlarge kernel,api dmlc/master

[mufeili]

A1 and A2 can be different. For example, for MLP, A1 is DAD, A2 is DA: https://github.com/CUAI/CorrectAndSmooth/blob/b910314a59270984f5e249462ee3faa815fc9a0c/run_experiments.py#L140

[mufeili]

LGTM