initialize WASI stdio handles to invalid for better error handling (#4092)

* initialize WASI stdio handles to invalid for better error handling
* implement os_invalid_raw_handle function for consistent invalid handle representation

core/shared/platform/common/posix/posix_file.c

@@ -1032,4 +1032,10 @@ char *
 os_realpath(const char *path, char *resolved_path)
 {
     return realpath(path, resolved_path);
-}
+}
+
+os_raw_file_handle
+os_invalid_raw_handle(void)
+{
+    return -1;
+}