Add Hyperbolic GCN layer of paper [Hyperbolic Graph Convolutional Neural Networks](https://arxiv.org/abs/1910.12933)

[Tokisakix]

From #1334 and #5453.

When I try to add HGCNConv layer (paper Hyperbolic Graph Convolutional Neural Networks) I discover that somebody had done it two years ago. Then I find and fix some bugs in #5453.

I also add test of HGCNConv, HypAct and HypLinear in poincareBall and hyperboloid two mod.

Moreover, I write an example of its use for giving people some idea of where it best applies.

[x] Add HGCNConv layer
[x] Add some test of HGCNConv, HypAct and HypLinear
[x] Add an example