refactor(api): give "hl_group" more accurate _meta type

These can either be number or string in lua, so we can specify this
directly as "number|string".

src/nvim/generators/gen_api_dispatch.lua

@@ -72,7 +72,6 @@ local keysets = {}
 local function add_keyset(val)
   local keys = {}
   local types = {}
-  local hlgroups = {}
   local is_set_name = 'is_set__' .. val.keyset_name .. '_'
   local has_optional = false
   for i, field in ipairs(val.fields) do
@@ -81,7 +80,6 @@ local function add_keyset(val)
     end
     if field.name ~= is_set_name and field.type ~= 'OptionalKeys' then
       table.insert(keys, field.name)
-      hlgroups[field.name] = field.name:find('hl_group') and true or false
     else
       if i > 1 then
         error("'is_set__{type}_' must be first if present")
@@ -97,7 +95,6 @@ local function add_keyset(val)
     name = val.keyset_name,
     keys = keys,
     types = types,
-    hlgroups = hlgroups,
     has_optional = has_optional,
   })
 end
@@ -285,7 +282,9 @@ for _, k in ipairs(keysets) do
   keysets_defs:write('extern KeySetLink ' .. k.name .. '_table[];\n')
 
   local function typename(type)
-    if type ~= nil then
+    if type == 'HLGroupID' then
+      return 'kObjectTypeInteger'
+    elseif type ~= nil then
       return 'kObjectType' .. type
     else
       return 'kObjectTypeNil'
@@ -311,7 +310,7 @@ for _, k in ipairs(keysets) do
         .. ', '
         .. ind
         .. ', '
-        .. (k.hlgroups[key] and 'true' or 'false')
+        .. (k.types[key] == 'HLGroupID' and 'true' or 'false')
         .. '},\n'
     )
   end