lexer: add error location to lexer errors

Before the change lexter errors did not report the location:

    $ nix build -f. mc
    error: path has a trailing slash
    (use '--show-trace' to show detailed location information)

Note that it's not clear what file generates the error.

After the change location is reported:

    $ src/nix/nix --extra-experimental-features nix-command build -f ~/nm mc
    error: path has a trailing slash

           at .../pkgs/development/libraries/glib/default.nix:54:18:

               53|   };
               54|   src = /tmp/foo/;
                 |                  ^
               55|
    (use '--show-trace' to show detailed location information)

Here we see both problematic file and the string itself.

0 files changed, 0 insertions, 0 deletions