keymap: add more (keypad) keycodes #9793

- K_KORIGIN instead of K_KCENTER: This name is similar to what is used
  by xev. Alternative could be K_KBEGIN as hinted here:
  https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h2-PC-Style-Function-Keys
  But I find Begin and Home too similar, and it might induced some
  confusion. The naming looked related to some old keyboard
  configuration.

- keymap.c: alias KPPeriod to kDel instead of kPoint.
  This might seems weird, but this is actually the behaviour that should
  be expected. libtermkey produces "KPPeriod" when num lock is off. To
  fix this would need to change this name in termkey.

closes #9780
closes #9793

src/nvim/keymap.h

@@ -256,9 +256,13 @@ enum key_extra {
 #define K_ZERO          TERMCAP2KEY(KS_ZERO, KE_FILLER)
 
 #define K_UP            TERMCAP2KEY('k', 'u')
+#define K_KUP           TERMCAP2KEY('K', 'u')   /* keypad up */
 #define K_DOWN          TERMCAP2KEY('k', 'd')
+#define K_KDOWN         TERMCAP2KEY('K', 'd')   /* keypad down */
 #define K_LEFT          TERMCAP2KEY('k', 'l')
+#define K_KLEFT         TERMCAP2KEY('K', 'l')   /* keypad left */
 #define K_RIGHT         TERMCAP2KEY('k', 'r')
+#define K_KRIGHT        TERMCAP2KEY('K', 'r')   /* keypad right */
 #define K_S_UP          TERMCAP2KEY(KS_EXTRA, KE_S_UP)
 #define K_S_DOWN        TERMCAP2KEY(KS_EXTRA, KE_S_DOWN)
 #define K_S_LEFT        TERMCAP2KEY('#', '4')
@@ -367,6 +371,7 @@ enum key_extra {
 #define K_PAGEDOWN      TERMCAP2KEY('k', 'N')
 #define K_KPAGEUP       TERMCAP2KEY('K', '3')   /* keypad pageup (upper R.) */
 #define K_KPAGEDOWN     TERMCAP2KEY('K', '5')   /* keypad pagedown (lower R.) */
+#define K_KORIGIN       TERMCAP2KEY('K', '2')   /* keypad center */
 
 #define K_KPLUS         TERMCAP2KEY('K', '6')   /* keypad plus */
 #define K_KMINUS        TERMCAP2KEY('K', '7')   /* keypad minus */