Ark: Control flow / some keyword completions aren't being populated

[DavisVaughan]

For example, function

Screen.Recording.2023-11-17.at.2.57.00.PM.mov

They are being purposefully skipped here:
https://github.com/posit-dev/amalthea/blob/435f95c4d5187832937ae68c52740be52510e54d/crates/ark/src/lsp/completions/session.rs#L605

I think it makes sense to skip them there and add them elsewhere or maybe to mark them as special types of completions from there (in particular handle break and next specially, i.e. not as functions!)