import { has_key } from "https://deno.land/x/denops_std@v5.0.2/function/mod.ts";
The result is a Number, which is TRUE if Dictionary {dict}
has an entry with key {key}. FALSE otherwise.
The {key} argument is a string. In Vim9 script a number is
also accepted (and converted to a string) but no other types.
In legacy script the usual automatic conversion to string is
done.
Can also be used as a method:
mydict->has_key(key)