Make wasi-nn backends as separated shared libraries (#3509)

- All files under *core/iwasm/libraries/wasi-nn* are compiled as shared libraries
- *wasi-nn.c* is shared between backends
- Every backend has a separated shared library
- If wasi-nn feature is enabled, iwasm will depend on shared library libiwasm.so
  instead of linking static library libvmlib.a

core/iwasm/common/wasm_native.c

@@ -33,9 +33,6 @@ get_spectest_export_apis(NativeSymbol **p_libc_builtin_apis);
 uint32
 get_libc_wasi_export_apis(NativeSymbol **p_libc_wasi_apis);
 
-uint32_t
-get_wasi_nn_export_apis(NativeSymbol **p_libc_wasi_apis);
-
 uint32
 get_base_lib_export_apis(NativeSymbol **p_base_lib_apis);
 
@@ -565,18 +562,6 @@ wasm_native_init()
         goto fail;
 #endif /* WASM_ENABLE_LIB_RATS */
 
-#if WASM_ENABLE_WASI_NN != 0
-    n_native_symbols = get_wasi_nn_export_apis(&native_symbols);
-#if WASM_ENABLE_WASI_EPHEMERAL_NN != 0
-#define wasi_nn_module_name "wasi_ephemeral_nn"
-#else /* WASM_ENABLE_WASI_EPHEMERAL_NN == 0 */
-#define wasi_nn_module_name "wasi_nn"
-#endif /* WASM_ENABLE_WASI_EPHEMERAL_NN != 0 */
-    if (!wasm_native_register_natives(wasi_nn_module_name, native_symbols,
-                                      n_native_symbols))
-        goto fail;
-#endif
-
 #if WASM_ENABLE_QUICK_AOT_ENTRY != 0
     if (!quick_aot_entry_init()) {
 #if WASM_ENABLE_SPEC_TEST != 0 || WASM_ENABLE_LIBC_BUILTIN != 0     \