Rename --codec to --video-codec

This prepares the introduction of --audio-codec.

app/src/options.h

@@ -99,7 +99,7 @@ struct scrcpy_options {
     const char *v4l2_device;
 #endif
     enum sc_log_level log_level;
-    enum sc_codec codec;
+    enum sc_codec video_codec;
     enum sc_record_format record_format;
     enum sc_keyboard_input_mode keyboard_input_mode;
     enum sc_mouse_input_mode mouse_input_mode;