[WIP] feat: support graph encoding backend auto-detection in wasi-nn

[TE-7000026184]

No description provided.

[TE-7000026184]

In current implementation of this PR, we assume that loading will fail if the format is not matched.
However, after checking some code, it seems the result of "load" function cannot indicate whether the file is in the correct format, for some back-ends, "load" functions only do some memory copy works.

Wondering whether there is an additional API for each back-end to check whether the model file is encoded in its way?
Plan B is to look into the content of the model file to be loaded. For "tflite" and "h5" format, header of the file contains magic number to verify the format, but "onnx" and some other formats do not have such things.