Non-equispaced Lagrange elements on simplices

[pbrubeck]

If we want to implement simplicial Lagrange elements with the recursive nodes from https://epubs.siam.org/doi/pdf/10.1137/20M1321802, should we implement them as a new class or could they be the extension of the 1D elements (GaussLegendre and GaussLobattoLegendre) that we already have?

[dham]

If the elements reduce to GL and GLL in 1D then please extend those elements. This will make integration in Firedrake more seamless

[pbrubeck]

Fixed by #46