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/aot/aot_runtime.c

@@ -1944,9 +1944,6 @@ aot_deinstantiate(AOTModuleInstance *module_inst, bool is_sub_inst)
 #endif
 
     if (!is_sub_inst) {
-#if WASM_ENABLE_WASI_NN != 0
-        wasi_nn_destroy((WASMModuleInstanceCommon *)module_inst);
-#endif
         wasm_native_call_context_dtors((WASMModuleInstanceCommon *)module_inst);
     }
 

core/iwasm/aot/aot_runtime.h

@@ -14,10 +14,6 @@
 #include "gc_export.h"
 #endif
 
-#if WASM_ENABLE_WASI_NN != 0
-#include "../libraries/wasi-nn/src/wasi_nn_private.h"
-#endif
-
 #ifdef __cplusplus
 extern "C" {
 #endif