add a set of apis to configure wasi-nn via InstantiationArgs2

[zhanheng1]

add a set of apis to configure wasi-nn via InstantiationArgs2:

1. Add a new command line option for wasi-nn: --wasi-nn-graph=encoding:target:model_path1:model_path2:...:model_pathN;
2. Add new structs to manage this cmd option: WASINNGlobalContext and wasi_nn_graph_registry;
3. Add 2 new parameters for load_by_name(encoding and target). load_by_name() can get encoding and target from WASINNGlobalContext and set into backend.
4. Update test codes.

[yamt]

shouldn't this be done before inst_args is used? ie. before wasm_runtime_instantiate_ex2

[zhanheng1]

If I recall correctly, we previously discussed this issue.
Since wasm_runtime_malloc() requires wasm_runtime_instantiate_ex2() to initialize the memory first, this logic should either be implemented inside wasm_runtime_instantiate_ex2(), or extracted as a separate function to be called after wasm_runtime_instantiate_ex2().
Originally, the function was placed in the middle of wasm_runtime_instantiate_ex2(), but it was later suggested that extracting it as a standalone function would be better, which is why the current version was adopted.

[yamt]

wasm_runtime_set_wasi_nn_registry is not supposed to be used by the embedder, is it?

i suppose the registry is passed via inst_args.

[zhanheng1]

If I remember correctly, we've also discussed this issue before.
Since inst_args is destroyed immediately in the next line of code, the WASM application cannot actually use it.
The current version stores the registry in a slot within each WASM module's context, allowing the WASM app to retrieve the registry via the module's context.
Therefore, wasm_runtime_set_wasi_nn_registry should be explicitly called in main.c.