[Refactor] Further decouple DLPack from DGL NDArray

[jermainewang]

🔨Work Item

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Project tracker: https://github.com/orgs/dmlc/projects/2

Description

The issue comes up from PR #4454 . The PR introduced a new data structure called DGLArray to replace DLTensor from DLPack. The follow up action is to further simplify the codebase. Considerations:

• Currrently, there are three classes dgl::runtime::NDArray, dgl::runtime::NDArray::Container and dgl::DGLArray. The question is whether we can consolidate them into one or two classes.
• Exposing DGL NDArray to Python adds another layer of complexity to the system. For example, there is a dgl/_ffi/runtime_ctypes.py::DGLArray python class. We need to further decouple it from DLPack and document clearly what each class is about.

@yaox12 let's use this thread for discussion.

Depending work items or issues

None

[github-actions[bot]]

This issue has been automatically marked as stale due to lack of activity. It will be closed if no further activity occurs. Thank you

[github-actions[bot]]

This issue has been automatically marked as stale due to lack of activity. It will be closed if no further activity occurs. Thank you