Move help commands to use more structure in signatures (#9949)

# Description

Signatures in `help commands` will now have more structure for params
and input/output pairs.

Example:

Improved params

![image](https://github.com/nushell/nushell/assets/547158/f5dacaf2-861b-4b44-aaa6-e17b4bcb953e)

Improved input/output pairs

![image](https://github.com/nushell/nushell/assets/547158/844a6e9c-dbfc-4c07-b0ef-fefd835a4cf0)


# User-Facing Changes

This is technically a breaking change if previous code assumed the shape
of things in `help commands`.

# Tests + Formatting
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crates/nu-protocol/src/plugin_signature.rs

@@ -12,12 +12,6 @@ pub struct PluginSignature {
     pub examples: Vec<PluginExample>,
 }
 
-impl std::fmt::Display for PluginSignature {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "{}", self.sig)
-    }
-}
-
 impl PluginSignature {
     pub fn new(sig: Signature, examples: Vec<PluginExample>) -> Self {
         Self { sig, examples }

crates/nu-protocol/src/signature.rs

@@ -124,72 +124,6 @@ pub struct Signature {
     pub category: Category,
 }
 
-/// Format argument type for user readable output.
-///
-/// In general:
-/// if argument type is a simple type(like string), we'll wrapped with `<>`, the result will be `<string>`
-/// if argument type is already contains `<>`, like `list<any>`, the result will be `list<any>`.
-fn fmt_type(arg_type: &Type, optional: bool) -> String {
-    let arg_type = arg_type.to_string();
-    if arg_type.contains('<') && arg_type.contains('>') {
-        if optional {
-            format!("{arg_type}?")
-        } else {
-            arg_type
-        }
-    } else if optional {
-        format!("<{arg_type}?>")
-    } else {
-        format!("<{arg_type}>")
-    }
-}
-
-// in general, a commands signature should looks like this:
-//
-// <string> | <string>, <int?> => string
-//
-// More detail explanation:
-// the first one is the input from previous command, aka, pipeline input
-// then followed by `|`, then positional arguments type
-// then optional arguments type, which ends with `?`
-// Then followed by `->`
-// Finally output type.
-//
-// If a command contains multiple input/output types, separate them in different lines.
-impl std::fmt::Display for Signature {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        let mut args = self
-            .required_positional
-            .iter()
-            .map(|p| fmt_type(&p.shape.to_type(), false))
-            .collect::<Vec<String>>();
-        args.append(
-            &mut self
-                .optional_positional
-                .iter()
-                .map(|p| fmt_type(&p.shape.to_type(), true))
-                .collect::<Vec<String>>(),
-        );
-        let args = args.join(", ");
-
-        let mut signatures = vec![];
-        for (input_type, output_type) in self.input_output_types.iter() {
-            // ident with two spaces for user friendly output.
-            let input_type = fmt_type(input_type, false);
-            let output_type = fmt_type(output_type, false);
-            if args.is_empty() {
-                signatures.push(format!("  {input_type} | {} -> {output_type}", self.name))
-            } else {
-                signatures.push(format!(
-                    "  {input_type} | {} {args} -> {output_type}",
-                    self.name
-                ))
-            }
-        }
-        write!(f, "{}", signatures.join("\n"))
-    }
-}
-
 impl PartialEq for Signature {
     fn eq(&self, other: &Self) -> bool {
         self.name == other.name