[RFC] Further Unify Packed and Object in TVM Runtime (#97)

This RFC proposes to further unify our PackedFunc and Object in TVM Runtime. The proposal builds on top of our past lessons and recont lessons from related project such as matxscript

The key improvements include: unifying type_code, solidifying AnyValue support for both stack and object values, open doors for small-string and NLP-preprocessing, and enable universal container.

Co-authored-by: Xiandi Ma <maxiandi@bytedance.com>
Co-authored-by: Junru Shao <junrushao1994@gmail.com>

* Address review comments

* Update per suggestion

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Co-authored-by: Xiandi Ma <maxiandi@bytedance.com>
Co-authored-by: Junru Shao <junrushao1994@gmail.com>