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

samples/inst-context/src/main.c

@@ -128,7 +128,7 @@ main(int argc, char *argv_main[])
     }
 
     wasm_function_inst_t func3 =
-        wasm_runtime_lookup_function(module_inst, "calculate", NULL);
+        wasm_runtime_lookup_function(module_inst, "calculate");
     if (!func3) {
         printf("The wasm function calculate is not found.\n");
         goto fail;