Add to use molecule 3D conformer

[OPAYA]

The 3D conformer coordinates are used in various model(SchNet, DimeNet, SpereNet, Graphormer).
Conformer generation code is added to contribute to more various model.

There are several methods of generating conformer provided by rdkit, but for now, the MMFF method was used.

[KiddoZhu]

Thanks! That's a good initiative. 3D conformers are really important for a wide range of tasks and models.

As conformer is not a necessary attribute to reconstruct a RDKit molecule, I would suggest reconsidering if we should put it as a precomputed attribute in data.Molecule.from_smiles or as a lazy attribute like data.Molecule.is_valid_rdkit. Additionally, providing an interface for different conformation generation methods would be nice.

We would come back to update your code and merge it.

[OPAYA]

Thanks for your response!

I considered because the conformer generation provided by Rdkit was not an accurate value.
Currently, I'm considering about implemented two versions of the conformers using rdkit's forcefield and the conformers calculated directly by the user through external software!