Remove unused argument in wasm_runtime_lookup_function and refactor WASMModuleInstance (#3218)

Remove the unused parameter `signature` from `wasm_runtime_lookup_function`.

Refactor the layout of WASMModuleInstance structure:
- move common data members `c_api_func_imports` and `cur_exec_env` from
  `WASMModuleInstanceExtraCommon` to `WASMModuleInstance`
- In `WASMModuleInstance`, enlarge `reserved[3]` to `reserved[5]` in case that
  we need to add more fields in the future

ps.
https://github.com/bytecodealliance/wasm-micro-runtime/issues/2530
https://github.com/bytecodealliance/wasm-micro-runtime/issues/3202

core/iwasm/include/wasm_export.h

@@ -616,13 +616,12 @@ wasm_runtime_get_wasi_exit_code(wasm_module_inst_t module_inst);
  *
  * @param module_inst the module instance
  * @param name the name of the function
- * @param signature the signature of the function, ignored currently
  *
  * @return the function instance found, NULL if not found
  */
 WASM_RUNTIME_API_EXTERN wasm_function_inst_t
 wasm_runtime_lookup_function(wasm_module_inst_t const module_inst,
-                             const char *name, const char *signature);
+                             const char *name);
 
 /**
  * Get parameter count of the function instance