Relax the closure syntax, highlight differently (#8846)

# Description

This relaxes the closure syntax so that `||` is no longer required. This
allows for `ls | each { $in.name }` for example.

I've gone ahead and changed the syntax highlighting so that blocks and
closures are distinct for now.

# User-Facing Changes

Removes `||` requirement for closures.

# 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
- `cargo run -- crates/nu-std/tests/run.nu` to run the tests for the
standard library

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```

# 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-color-config/src/shape_color.rs

@@ -9,6 +9,7 @@ pub fn default_shape_color(shape: String) -> Style {
         "shape_binary" => Style::new().fg(Color::Purple).bold(),
         "shape_block" => Style::new().fg(Color::Blue).bold(),
         "shape_bool" => Style::new().fg(Color::LightCyan),
+        "shape_closure" => Style::new().fg(Color::Green).bold(),
         "shape_custom" => Style::new().fg(Color::Green),
         "shape_datetime" => Style::new().fg(Color::Cyan).bold(),
         "shape_directory" => Style::new().fg(Color::Cyan),