[FFI] Introduce FFI reflection support in python

[tqchen]

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This PR brings up new reflection support in python. The new reflection now directly attaches property and methods to the class object themselves, making more efficient accessing than old mechanism.

It will also support broader set of value types that are compatible with the FFI system.

For now the old mechanism and new mechanism will co-exist, and we will phase out old mechanism as we migrate most needed features into new one.