vim-patch:8.2.4911: the mode #defines are not clearly named (#18499)

Problem:    The mode #defines are not clearly named.
Solution:   Prepend MODE_.  Renumber them to put the mapped modes first.
249591057b

A hunk from the patch depends on patch 8.2.4861, which hasn't been
ported yet, but that should be easy to notice.

src/nvim/input.c

@@ -39,7 +39,7 @@ int ask_yesno(const char *const str, const bool direct)
   const int save_State = State;
 
   no_wait_return++;
-  State = CONFIRM;  // Mouse behaves like with :confirm.
+  State = MODE_CONFIRM;  // Mouse behaves like with :confirm.
   setmouse();  // Disable mouse in xterm.
   no_mapping++;
   allow_keys++;  // no mapping here, but recognize keys
@@ -235,7 +235,7 @@ int prompt_for_number(int *mouse_used)
   save_cmdline_row = cmdline_row;
   cmdline_row = 0;
   save_State = State;
-  State = ASKMORE;  // prevents a screen update when using a timer
+  State = MODE_ASKMORE;  // prevents a screen update when using a timer
   // May show different mouse shape.
   setmouse();