Better generic errors for plugins (and perhaps scripts) (#12236)

# Description
This makes `LabeledError` much more capable of representing close to
everything a `miette::Diagnostic` can, including `ShellError`, and
allows plugins to generate multiple error spans, codes, help, etc.

`LabeledError` is now embeddable within `ShellError` as a transparent
variant.

This could also be used to improve `error make` and `try/catch` to
reflect `LabeledError` exactly in the future.

Also cleaned up some errors in existing plugins.

# User-Facing Changes
Breaking change for plugins. Nicer errors for users.

crates/nu_plugin_inc/src/nu/mod.rs

@@ -1,9 +1,7 @@
 use crate::inc::SemVerAction;
 use crate::Inc;
-use nu_plugin::{
-    EngineInterface, EvaluatedCall, LabeledError, Plugin, PluginCommand, SimplePluginCommand,
-};
-use nu_protocol::{ast::CellPath, PluginSignature, SyntaxShape, Value};
+use nu_plugin::{EngineInterface, EvaluatedCall, Plugin, PluginCommand, SimplePluginCommand};
+use nu_protocol::{ast::CellPath, LabeledError, PluginSignature, SyntaxShape, Value};
 
 pub struct IncPlugin;