Previously, the built-in language server client checked if the first
argument of cmd was executable via vim.fn.executable. This ignores PATH
injected via cmd_env. Instead, we now start the client via uv.spawn, and
handle the failure mode, reporting the error back to the user.
Co-authored-by: Mathias Fußenegger <mfussenegger@users.noreply.github.com>
1a60580925
