PluginList
PluginList = readonly (
Plugin|Omission|PluginList|false|null|undefined)[]
What Game and createGameWorld take: plugins, omits made with
omit, and lists of them. A list inside the list counts as its
entries in place, at any depth, and a false, null or undefined
entry is skipped, so hardMode && hardModeRules is an entry that adds
its rules only in hard mode.