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/aot/aot_runtime.c

@@ -1083,6 +1083,17 @@ aot_instantiate(AOTModule *module, bool is_sub_inst, uint32 stack_size,
     }
 #endif
 
+#if WASM_ENABLE_WASI_NN != 0
+    if (!is_sub_inst) {
+        if (!(((AOTModuleInstanceExtra *)module_inst->e)->wasi_nn_ctx =
+                  wasi_nn_initialize())) {
+            set_error_buf(error_buf, error_buf_size,
+                          "wasi nn initialization failed");
+            goto fail;
+        }
+    }
+#endif
+
     /* Initialize the thread related data */
     if (stack_size == 0)
         stack_size = DEFAULT_WASM_STACK_SIZE;
@@ -1194,6 +1205,15 @@ aot_deinstantiate(AOTModuleInstance *module_inst, bool is_sub_inst)
         wasm_runtime_free(
             ((AOTModuleInstanceExtra *)module_inst->e)->c_api_func_imports);
 
+#if WASM_ENABLE_WASI_NN != 0
+    if (!is_sub_inst) {
+        WASINNContext *wasi_nn_ctx =
+            ((AOTModuleInstanceExtra *)module_inst->e)->wasi_nn_ctx;
+        if (wasi_nn_ctx)
+            wasi_nn_destroy(wasi_nn_ctx);
+    }
+#endif
+
     wasm_runtime_free(module_inst);
 }