Inlay hints (aka Parameter hints)

[jestarray]

jeapostrophe/racket-langserver#29

(bug regarding wrong argument order)
racket/racket@96f26e0

Rendering inlay hints would be very useful, eliminating a lot of the guess work of function arguments and struct fields without needing to look at the documentation or the definition again and in the case of structs, creating functions with keyword arguments to see what the fields are.

(struct person (firstname middlename lastname age job))

; when constructing, it will render the field names as a sort of "background image", 
; the code that actually is ran is the valid amount of arguments, so (person "bob" "j" "smith" 20 "programmer")

(person firstname "bob" middlename "j" lastname "smith" age 20 job "programmer")