refactor(gen_events): sort enums case-insensitively (#32811)

This actually only affects the order in which Cmdline* and Cmdwin*
autocommands are listed, and it appears that the names of Cmdwin* were
changed to CmdWin* in 8ed2dbf6e2 without
explanation.

Also, remove the final NULL element from the names table.

src/gen/gen_events.lua

@@ -8,7 +8,9 @@ local aliases = auevents.aliases
 
 --- @type string[]
 local names = vim.tbl_keys(vim.tbl_extend('error', events, aliases))
-table.sort(names)
+table.sort(names, function(a, b)
+  return a:lower() < b:lower()
+end)
 
 local enum_tgt = assert(io.open(fileio_enum_file, 'w'))
 local names_tgt = assert(io.open(names_file, 'w'))
@@ -22,7 +24,7 @@ static const struct event_name {
   size_t len;
   char *name;
   int event;
-} event_names[] = {]])
+} event_names[NUM_EVENTS] = {]])
 
 for i, name in ipairs(names) do
   enum_tgt:write(('\n  EVENT_%s = %u,'):format(name:upper(), i - 1))
@@ -45,11 +47,10 @@ enum_tgt:write(('\n  NUM_EVENTS = %u,'):format(#names))
 enum_tgt:write('\n} event_T;\n')
 enum_tgt:close()
 
-names_tgt:write('\n  [NUM_EVENTS] = {0, NULL, (event_T)0},\n};\n')
+names_tgt:write('\n};\n')
 names_tgt:write('\nstatic AutoCmdVec autocmds[NUM_EVENTS] = { 0 };\n')
 
 local hashorder = vim.tbl_map(string.lower, names)
-table.sort(hashorder)
 local hashfun
 hashorder, hashfun = hashy.hashy_hash('event_name2nr', hashorder, function(idx)
   return 'event_names[event_hash[' .. idx .. ']].name'

src/nvim/autocmd.c

@@ -2267,7 +2267,7 @@ char *set_context_in_autocmd(expand_T *xp, char *arg, bool doautocmd)
   return NULL;
 }
 
-// Function given to ExpandGeneric() to obtain the list of event names.
+/// Function given to ExpandGeneric() to obtain the list of event names.
 char *expand_get_event_name(expand_T *xp, int idx)
 {
   (void)xp;  // xp is a required parameter to be used with ExpandGeneric
@@ -2283,14 +2283,23 @@ char *expand_get_event_name(expand_T *xp, int idx)
     return name;
   }
 
+  int i = idx - next_augroup_id;
+  if (i < 0 || i >= NUM_EVENTS) {
+    return NULL;
+  }
+
   // List event names
-  return event_names[idx - next_augroup_id].name;
+  return event_names[i].name;
 }
 
 /// Function given to ExpandGeneric() to obtain the list of event names. Don't
 /// include groups.
 char *get_event_name_no_group(expand_T *xp FUNC_ATTR_UNUSED, int idx, bool win)
 {
+  if (idx < 0 || idx >= NUM_EVENTS) {
+    return NULL;
+  }
+
   if (!win) {
     return event_names[idx].name;
   }