Evaluate where get_path() and friends belong

[jennybc]

Is devtools still the forever home for get_path(), set_path(path), and add_path(path, after = Inf)? I came across these in a disambiguation prompt when seeking help on fs::path(). The latter two definitely feel more like withr functions now.

[jimhester]

withr has with_path(), so you can get the same behavior as add_path(after = Inf) with withr::with_path(path, action = "suffix").

It doesn't seem like these functions are used by any packages on CRAN (including devtools) so maybe we should just remove them entirely?

[jennybc]

I can convince myself either way, but The Great Devtools Breakup certainly feels like a good time to clean out the proverbial closet.