refactor(api): use an arena for nvim_buf_get_lines and buffer updates

Refactor some earlier "temporary Array" code in buffer_updates.c to use
the modern style of MAXSIZE_TEMP_ARRAY and ADD_C

src/nvim/generators/gen_api_dispatch.lua

@@ -55,15 +55,15 @@ local function add_function(fn)
       -- for specifying errors
       fn.parameters[#fn.parameters] = nil
     end
+    if #fn.parameters ~= 0 and fn.parameters[#fn.parameters][1] == 'lstate' then
+      fn.has_lua_imp = true
+      fn.parameters[#fn.parameters] = nil
+    end
     if #fn.parameters ~= 0 and fn.parameters[#fn.parameters][1] == 'arena' then
       -- return value is allocated in an arena
       fn.arena_return = true
       fn.parameters[#fn.parameters] = nil
     end
-    if #fn.parameters ~= 0 and fn.parameters[#fn.parameters][1] == 'lstate' then
-      fn.has_lua_imp = true
-      fn.parameters[#fn.parameters] = nil
-    end
   end
 end