Ark: Completion engine should know more about `?`

[DavisVaughan]

• To be able to avoid adding () and showing parameter hints when completing functions Console: Conflict between Accept Suggestion/Execute #550 (comment)
• To be able to show links to topics when ? is active (also hook that up to help() through a custom completion) Tracked in Include help topics in completions for ? #6157 now

It's probably time to introduce a CompletionOption struct to contain something like in_help: bool and promise_strategy: Option<PromiseStrategy> which gets fed through all of the completion functions as an immutable reference. If a particular completion source needs to tweak the option struct, it would clone it first, tweak it, and then pass it down to the completion item helpers.