vim-patch:8.2.2454: leading space can not be made visible (#14138)

Problem:    Leading space can not be made visible.
Solution:   Add "lead:" to 'listchars'. (closes vim/vim#7772)
91478ae49a

src/nvim/buffer_defs.h

@@ -1201,6 +1201,7 @@ struct window_S {
     int tab1;                       ///< first tab character
     int tab2;                       ///< second tab character
     int tab3;                       ///< third tab character
+    int lead;
     int trail;
     int conceal;
   } w_p_lcs_chars;