Move server-related code to server.c

The file server.c already existed, but exposed a low-level API. Make it
higher-level, so that scrcpy.c does not handle server details directly.

app/src/command.h

@@ -42,4 +42,8 @@ process_t adb_reverse(const char *serial, const char *device_socket_name, uint16
 process_t adb_reverse_remove(const char *serial, const char *device_socket_name);
 process_t adb_push(const char *serial, const char *local, const char *remote);
 
+// convenience function to wait for a successful process execution
+// automatically log process errors with the provided process name
+SDL_bool process_check_success(process_t process, const char *name);
+
 #endif