Simple extended space cadet (#5277)

* Simplifying and Extending Space Cadet to work on Ctrl and Alt keys

* PR Review feedback

* Reverting back to keycodes

common_features.mk

@@ -351,3 +351,9 @@ ifeq ($(strip $(OLED_DRIVER_ENABLE)), yes)
     QUANTUM_LIB_SRC += i2c_master.c
     SRC += oled_driver.c
 endif
+
+SPACE_CADET_ENABLE ?= yes
+ifeq ($(strip $(SPACE_CADET_ENABLE)), yes)
+  SRC += $(QUANTUM_DIR)/process_keycode/process_space_cadet.c
+  OPT_DEFS += -DSPACE_CADET_ENABLE
+endif