feat: support building on iOS platform (#3033)

frontend/appflowy_flutter/packages/appflowy_backend/ios/Classes/binding.h

@@ -0,0 +1,18 @@
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+int64_t init_sdk(char *path);
+
+void async_event(int64_t port, const uint8_t *input, uintptr_t len);
+
+const uint8_t *sync_event(const uint8_t *input, uintptr_t len);
+
+int32_t set_stream_port(int64_t port);
+
+void link_me_please(void);
+
+void backend_log(int64_t level, const char *data);
+
+void set_env(const char *data);