Autocomplete of methods for given variables

[krystophny]

Recently, the PR https://github.com/JuliaLang/julia/pull/38791 for the REPL got merged to be included in the next Julia version. This means that the REPL will tab-complete statements like ?(x, y) to yield all methods that apply to x and y as well as ?(x with arbitrary additional arguments. It would be nice to have this also in the language server for use in VSCode and other editors. The current discussion is on https://discourse.julialang.org/t/tab-completion-to-find-methods-for-given-variable-s/66076