Improvements re: completing function as reference vs call

[jennybc]

I think the last rounds of improvement re: function completions were in #819 and #754. For now, the heuristic for deciding whether to treat as a function reference vs. call is based on whether we're inside a list of special functions:

ark/crates/ark/src/lsp/completions/function_context.rs

Lines 158 to 166 in 1577d04

	static FUNCTIONS_EXPECTING_A_FUNCTION_REFERENCE: &[&str] = &[
	"args",
	"debug",
	"debugonce",
	"formals",
	"help",
	"trace",
	"str",
	];

Two examples of sites where a user wants a function reference (but gets parentheses anyway) came up in posit-dev/positron#9044 (comment)

library(tidyverse)

penguins |> relocate(where(is.character()))
map(1:3, mean())

The current list only contains functions from the base and utils packages. But tidyselect::where() is a pretty clearcut case. More complicated, but also compelling is purrr::map() (and base equivalents). Not sure which will come first: improving the ad hoc list or improving the whole approach, but opening this as a place to track concrete examples that folks mention.