Refactor WASI-NN to simplify support for multiple frameworks

[tonibofarull]

• Reorganize library structure.
• Use latest version of wasi-nn wit (Oct 25, 2022): https://github.com/WebAssembly/wasi-nn/blob/0f77c48ec195748990ff67928a4b3eef5f16c2de/wasi-nn.wit.md
• Split logic that converts WASM structs to native structs in a separate file.
• Simplify addition of new frameworks.

[tonibofarull]

TODO

• Free mem of NNs used by an app on exit.

[wenyongh]

TODO

• Free mem of NNs used by an app on exit.

@tonibofarull Have you finished this item and shall I merge the PR?
@yamt Are there any comments from you?

[tonibofarull]

@wenyongh, I still need to check how it's done in wasi fdtable teardown.
We can proceed as you want:

• Keep the PR open until I finish this topic.
• Merge this and do it in another PR.

Thank you!

[wenyongh]

@wenyongh, I still need to check how it's done in wasi fdtable teardown. We can proceed as you want:

• Keep the PR open until I finish this topic.
• Merge this and do it in another PR.

Thank you!

Got it, had better keep the PR open until you finish it. Thanks.

[tonibofarull]

Fixed the warnings.
Only tensorflow specific are appearing and this one:

/home/wamr/core/iwasm/libraries/wasi-nn/wasi_nn.h:126:5: warning: 'import_module' attribute directive ignored [-Wattributes]
  126 |     __attribute__((import_module("wasi_nn")));
      |     ^~~~~~~~~~~~~
/home/wamr/core/iwasm/libraries/wasi-nn/wasi_nn.h:145:5: warning: 'import_module' attribute directive ignored [-Wattributes]
  145 |     __attribute__((import_module("wasi_nn")));
      |     ^~~~~~~~~~~~~
/home/wamr/core/iwasm/libraries/wasi-nn/wasi_nn.h:157:5: warning: 'import_module' attribute directive ignored [-Wattributes]
  157 |     __attribute__((import_module("wasi_nn")));

which corresponds to the import but needed in the linkage with the WASM code.

[tonibofarull]

As stated here #1573, the next step will be to add GPU support.
Later on, I'll add the wasi-nn context per WASM app and supporting multiple networks at the same time.

Also, I'll work on checking the C/C++ bindings bytecodealliance/wasi-nn#75

[tonibofarull]

• Ready for review

[wenyongh]

• Ready for review

@tonibofarull The coding guideline CI check failed for wasi_nn.c, could you use clang-format-12 to format the file?

sudo apt-get install clang-format-12
clang-format-12 -i --style=file path/to/file

Refer to:
https://github.com/bytecodealliance/wasm-micro-runtime/actions/runs/3996791726/jobs/6857274884

Use `clang-format-12` or `git-clang-format-12` to check code format of
    the PR, with a commit range specified. It is required to format the
    code before committing the PR, or it might fail to pass the CI check:

    1. Install clang-format-12.0.0
    Normally we can install it by `sudo apt-get install clang-format-12`,
    or download the `clang+llvm-12.0.0-xxx-tar.xz` package from
      https://github.com/llvm/llvm-project/releases/tag/llvmorg-12.0.0
    and install it

    2. Format the C/C++ source file
    ``` shell
    cd path/to/wamr/root
    clang-format-12 --style file -i path/to/file
    ```

[tonibofarull]

@tonibofarull The coding guideline CI check failed for wasi_nn.c, could you use clang-format-12 to format the file?

I was using the general version (no -12).