Add pattern matching (#8590)

# Description

This adds `match` and basic pattern matching.

An example:

```
match $x {
  1..10 => { print "Value is between 1 and 10" }
  { foo: $bar } => { print $"Value has a 'foo' field with value ($bar)" }
  [$a, $b] => { print $"Value is a list with two items: ($a) and ($b)" }
  _ => { print "Value is none of the above" }
}
```

Like the recent changes to `if` to allow it to be used as an expression,
`match` can also be used as an expression. This allows you to assign the
result to a variable, eg) `let xyz = match ...`

I've also included a short-hand pattern for matching records, as I think
it might help when doing a lot of record patterns: `{$foo}` which is
equivalent to `{foo: $foo}`.

There are still missing components, so consider this the first step in
full pattern matching support. Currently missing:
* Patterns for strings
* Or-patterns (like the `|` in Rust)
* Patterns for tables (unclear how we want to match a table, so it'll
need some design)
* Patterns for binary values
* And much more

# User-Facing Changes

[see above]

# 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

> **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-command/src/formats/to/json.rs

@@ -127,7 +127,10 @@ pub fn value_to_json_value(v: &Value) -> Result<nu_json::Value, ShellError> {
 
         Value::List { vals, .. } => nu_json::Value::Array(json_list(vals)?),
         Value::Error { error } => return Err(*error.clone()),
-        Value::Closure { .. } | Value::Block { .. } | Value::Range { .. } => nu_json::Value::Null,
+        Value::Closure { .. }
+        | Value::Block { .. }
+        | Value::Range { .. }
+        | Value::MatchPattern { .. } => nu_json::Value::Null,
         Value::Binary { val, .. } => {
             nu_json::Value::Array(val.iter().map(|x| nu_json::Value::U64(*x as u64)).collect())
         }

crates/nu-command/src/formats/to/nuon.rs

@@ -246,6 +246,12 @@ pub fn value_to_string(
                 ))
             }
         }
+        Value::MatchPattern { .. } => Err(ShellError::UnsupportedInput(
+            "match patterns are currently not nuon-compatible".to_string(),
+            "value originates from here".into(),
+            span,
+            v.expect_span(),
+        )),
         Value::Nothing { .. } => Ok("null".to_string()),
         Value::Range { val, .. } => Ok(format!(
             "{}..{}{}",

crates/nu-command/src/formats/to/text.rs

@@ -153,6 +153,7 @@ fn local_into_string(value: Value, separator: &str, config: &Config) -> String {
         Value::Binary { val, .. } => format!("{val:?}"),
         Value::CellPath { val, .. } => val.into_string(),
         Value::CustomValue { val, .. } => val.value_string(),
+        Value::MatchPattern { val, .. } => format!("{:?}", val),
     }
 }
 

crates/nu-command/src/formats/to/toml.rs

@@ -93,6 +93,7 @@ fn helper(engine_state: &EngineState, v: &Value) -> Result<toml::Value, ShellErr
                 .collect::<Result<Vec<toml::Value>, ShellError>>()?,
         ),
         Value::CustomValue { .. } => toml::Value::String("<Custom Value>".to_string()),
+        Value::MatchPattern { .. } => toml::Value::String("<Match Pattern>".to_string()),
     })
 }
 

crates/nu-command/src/formats/to/yaml.rs

@@ -97,6 +97,7 @@ pub fn value_to_yaml_value(v: &Value) -> Result<serde_yaml::Value, ShellError> {
                 .collect::<Result<Vec<serde_yaml::Value>, ShellError>>()?,
         ),
         Value::CustomValue { .. } => serde_yaml::Value::Null,
+        Value::MatchPattern { .. } => serde_yaml::Value::Null,
     })
 }