# Description
Before this PR, errors without error codes are printed somewhat
strangely, with the `×` and the description being printed on the same
line as the `Error:` text:

    Error:   × Invalid literal
       ╭─[entry #1:1:2]
     1 │ "\z"
       ·  ─┬─
       ·   ╰── unrecognized escape after '\' in string
       ╰────


This PR adds a default error code for the different error types:

    Error: nu::parser::error

      × Invalid literal
       ╭─[entry #1:1:2]
     1 │ "\z"
       ·  ─┬─
       ·   ╰── unrecognized escape after '\' in string
       ╰────

While maybe not as informative as a proper error code, it makes
`GenericError`s and other things which don't have error codes look a lot
nicer.

It would be nicer if we could just set `diagnostic(code:
"nu:🐚:error")` at the top of `ShellError`, but unfortunately you
can't set a "default" at the `enum` level and then override it in the
variants. @cptpiepmatz mentioned he might change miette's derive macro
to accommodate this, in that case we can switch the approach here.

# User-Facing Changes
* Errors without error codes now have a default error code corresponding
to from which part of Nushell the error occurred (shell, parser,
compile, etc)

---------

Co-authored-by: Bahex <17417311+Bahex@users.noreply.github.com>