Add EGNNConv support for HeteroGraphConv

[rbSparky]

Covers Issue #311

This is a work in progress, just wanted to make sure I am on the right track

Since EGNNConv has H as input as well I added another function:

function (hgc::HeteroGraphConv)(g::GNNHeteroGraph, x::NamedTuple, h::AbstractMatrix)
    function forw(l, et)
        sg = edge_type_subgraph(g, et)
        node1_t, _, node2_t = et

        x_features = (x[node1_t], x[node2_t])
        h_features = h # temporary

        return l(sg, h_features, x_features)
    end
    outs = [forw(l, et) for (l, et) in zip(hgc.layers, hgc.etypes)]
    dst_ntypes = [et[3] for et in hgc.etypes]
    return _reduceby_node_t(hgc.aggr, outs, dst_ntypes)
end

Let me know if there is an alternative like using the arg in the old function (pass as a Dict) but this just seemed more convenient.

Will add more updates and test in the coming days. Will remove all debug statements when done.

[CarloLucibello]

is there an idea or some effort planned in fixing this? Otherwise better close so that it won't prevent other people from working on it

[rbSparky]

is there an idea or some effort planned in fixing this? Otherwise better close so that it won't prevent other people from working on it

Yes, currently I'm trying to make it work.
I'll close it if there is no progress

[rbSparky]

Could you confirm if I'm on the right path?
Thanks