Move SENDSTRING_BELL code to send_string.h (#13566)

quantum/send_string.c

@@ -20,6 +20,14 @@
 
 #include "send_string.h"
 
+#if defined(AUDIO_ENABLE) && defined(SENDSTRING_BELL)
+#    include "audio.h"
+#    ifndef BELL_SOUND
+#        define BELL_SOUND TERMINAL_SOUND
+#    endif
+float bell_song[][2] = SONG(BELL_SOUND);
+#endif
+
 // clang-format off
 
 /* Bit-Packed look-up table to convert an ASCII character to whether