Clean up keyword lines in help (#7243)

# Description

This makes the help messages cleaner for keyword-style arguments.

Before:
```
  (optional) else_expression <Keyword([101, 108, 115, 101], Expression)>: expression or block to run if check fails
```

Now:
```
  (optional) "else" + <expression>: expression or block to run if check fails
```


# User-Facing Changes

Changes how help is printed, so we use slightly different shape names

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-command/src/core_commands/try_.rs

@@ -20,7 +20,7 @@ impl Command for Try {
             .input_output_types(vec![(Type::Any, Type::Any)])
             .required("try_block", SyntaxShape::Block, "block to run")
             .optional(
-                "else_expression",
+                "catch_block",
                 SyntaxShape::Keyword(
                     b"catch".to_vec(),
                     Box::new(SyntaxShape::Closure(Some(vec![SyntaxShape::Any]))),