[Bug] Relay/TOPI `adv_index` not supporting `None` as arguments

[shingjan]

The advanced indexing implementation of relay/topi is not able to handle cases that use None as one of the indexing argument.

My repro under test_forward_index

    class Index2(Module):
        def forward(self, x):
            return x[None, [2, 2]]

    input_data = torch.rand([3, 3, 3, 3]).float().cpu()
    verify_model_with_input(Index2().eval(), [input_data])

Expected behavior

A tensor shaped [1, 2, 3, 3, 3] shall be returned.

Actual behavior

>           raise Exception("warning unhandled case: {0}".format(type(expr)))
E           Exception: warning unhandled case: <class 'NoneType'>

python/tvm/relay/expr_functor.py:76: Exception

Environment

Latest TVM main

cc: @masahi