Snapshot release 2023-03-01

Features

• Better completions, documentations and types for builtins.
  Now builtins.| completes correctly with signatures and
  documentations.

• Virtual path support. This is used by VSCode or coc.nvim when editing
  a new untitled file with filetype set to nix.

• A coc.nvim extension coc-nil under editors/coc-nil for simpler
  startup. Currently it is still working in progress and does nothing
  more than passing coc.nvim configurations to the LSP.

  The extension is exported as flake output package coc-nil, or
  vimPlugins.coc-nil when using overlays.

Fixes

• follows resolution of flake locks.
• Panics when flake_graph is accessed but not set.
• Documentation typos.