[Utils] Node homophily measure

[mufeili]

Description

I'll implement the rest two measures once everyone is comfortable with the practice in this PR.

Checklist

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [$CATEGORY] (such as [NN], [Model], [Doc], [Feature]])
• I've leverage the tools to beautify the python and c++ code.
• The PR is complete and small, read the Google eng practice (CL equals to PR) to understand more about small PR. In DGL, we consider PRs with less than 200 lines of core code change are small (example, test and documentation could be exempted).
• All changes have test coverage
• Code is well-documented
• To the best of my 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

[dgl-bot]

Commit ID: 3e66773

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Commit ID: 4aac2dd

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Commit ID: 20dcaa875108993281e8ceaab8e7ec6f8eff81d7

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Commit ID: d5f77263e7dd1fb501068f2318419d42b8fc2f44

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Commit ID: 8f690ce4e8ceed1c63f71b67fe8c55f0ecc3378b

Build ID: 7

Status: ✅ CI test succeeded.

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Commit ID: 50ec561

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Commit ID: 50ec561

Build ID: 9

Status: ✅ CI test succeeded.

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