support Rust LSP server auto-detect some useful root path based on location of Cargo.toml
Summary:
now for me rls works for some imple project like
https://github.com/rust-lang/rustfmt
Reviewers: mnauwelaerts
Subscribers: dhaumann, univerz, kwrite-devel
Tags: Kate
Differential Revision: https://phabricator.kde.org/D22963