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/libraries/wasi-nn/wasi_nn.cmake

@@ -5,6 +5,15 @@ set (WASI_NN_DIR ${CMAKE_CURRENT_LIST_DIR})
 
 add_definitions (-DWASM_ENABLE_WASI_NN=1)
 
-set (LIBC_WASI_NN_SOURCE ${WASI_NN_DIR}/wasi_nn_native.c ${WASI_NN_DIR}/wasi_nn_tensorflow.cpp)
+include_directories (${WASI_NN_DIR})
+include_directories (${WASI_NN_DIR}/src)
+include_directories (${WASI_NN_DIR}/src/utils)
+
+set (
+    LIBC_WASI_NN_SOURCE
+    ${WASI_NN_DIR}/src/wasi_nn.c
+    ${WASI_NN_DIR}/src/wasi_nn_tensorflowlite.cpp
+    ${WASI_NN_DIR}/src/utils/wasi_nn_app_native.c
+)
 
 set (TENSORFLOW_LIB tensorflow-lite)