[Performance] Add option to not validate graph node count

[GMNGeoffrey]

Description

The node count validation forces a device/host sync and can have a significant performance penalty. The argument I added mirrors one on create_block added in #7240. Seems like someone saw the same performance issue there.

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. I did not find any existing coverage for this function
• 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

[GMNGeoffrey]

@mfbalin @frozenbugs @BarclayII PTAL (I can't add reviewers)