Refactor WASI-NN to simplify the support for multiple frameworks (#1834)

- Reorganize the library structure
- Use the latest version of `wasi-nn` wit (Oct 25, 2022):
    0f77c48ec1/wasi-nn.wit.md
- Split logic that converts WASM structs to native structs in a separate file
- Simplify addition of new frameworks

core/iwasm/interpreter/wasm_runtime.h

@@ -11,6 +11,10 @@
 #include "../common/wasm_runtime_common.h"
 #include "../common/wasm_exec_env.h"
 
+#if WASM_ENABLE_WASI_NN != 0
+#include "../libraries/wasi-nn/src/wasi_nn_private.h"
+#endif
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -242,6 +246,10 @@ typedef struct WASMModuleInstanceExtra {
         && WASM_ENABLE_LAZY_JIT != 0)
     WASMModuleInstance *next;
 #endif
+
+#if WASM_ENABLE_WASI_NN != 0
+    WASINNContext *wasi_nn_ctx;
+#endif
 } WASMModuleInstanceExtra;
 
 struct AOTFuncPerfProfInfo;