Generate rust-project.json for rust-analyzer

[dcbaker]

Rust-analyzer is the official, upstream, ide frontend for Rust. It generally assumes that you're using cargo, but provides a mechanism for other builds systems in the form of a rust-project.json, which rust-analyzer understands, much like many C/C++ linters understand compile_commands.json.

It uses a rust-analyzer specific format, but one that meson has all of the information necessary to generate at configure time, and given it's popularity is probably worth doing.