[util] add `tvm.support.dump_for_debug` function

[cconvey]

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• add a utility function to help with debugging / investigation

  The function is particularly geared to help programmers examine changes to TVM modules and functions as they progress through the scheduling and lowering.

[cconvey]

I find this function helpful for my own development work. I'm not positive that tvm/support.py is the best home for it, but it would be nice to have it around.

[cconvey]

@areusch : This seems like the kind of thing you'd have thoughts on :)

[areusch]

i definitely don't dislike this, but it kinda seems like it should be a method on ObjectRef or ObjectRef.__str__ should handle this rather than be a separate function in tvm.support. could you suggest some improvements to the existing __str__ or __repr__ or functionality in src/printer? cc @yelite