[PyG] Support direct data loading from PyG Data&HeteroData format

[husimplicity]

🚀 The feature, motivation and pitch

To leverage pre-processing modules and datasets from PyG, we need to implement a data loading function that transforms PyG Data&HeteroData format to GLT's format. The function is expected to be convenient and concise for users.

Alternatives

No response

Additional context

No response