Adds default value for TAPPING_TERM if Tap Dance is enabled (#2785)

* Force require TAPPING_TERM if Tap Dance is enabled

* Handle lack of TAPPING_TERM more gracefully

quantum/process_keycode/process_tap_dance.c

@@ -16,6 +16,10 @@
 #include "quantum.h"
 #include "action_tapping.h"
 
+#ifndef TAPPING_TERM
+#define TAPPING_TERM 200
+#endif
+
 #ifndef NO_ACTION_ONESHOT
 uint8_t get_oneshot_mods(void);
 #endif

quantum/quantum.h

@@ -108,7 +108,9 @@ extern uint32_t default_layer_state;
     #include "process_unicodemap.h"
 #endif
 
+#ifdef TAP_DANCE_ENABLE
   #include "process_tap_dance.h"
+#endif
 
 #ifdef PRINTING_ENABLE
     #include "process_printer.h"