[Core] Add Repeat Key ("repeat last key") as a core feature. (#19700)

Co-authored-by: casuanoob <96005765+casuanoob@users.noreply.github.com>
Co-authored-by: Sergey Vlasov <sigprof@gmail.com>

builddefs/generic_features.mk

@@ -32,6 +32,7 @@ GENERIC_FEATURES = \
     KEY_OVERRIDE \
     LEADER \
     PROGRAMMABLE_BUTTON \
+    REPEAT_KEY \
     SECURE \
     SPACE_CADET \
     SWAP_HANDS \

builddefs/show_options.mk

@@ -85,7 +85,8 @@ OTHER_OPTION_NAMES = \
   SECURE_ENABLE \
   CAPS_WORD_ENABLE \
   AUTOCORRECT_ENABLE \
-  TRI_LAYER_ENABLE
+  TRI_LAYER_ENABLE \
+  REPEAT_KEY_ENABLE
 
 define NAME_ECHO
        @printf "  %-30s = %-16s # %s\\n" "$1" "$($1)" "$(origin $1)"