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-protocol/src/syntax_shape.rs

@@ -73,6 +73,12 @@ pub enum SyntaxShape {
     /// A general math expression, eg `1 + 2`
     MathExpression,
 
+    /// A block of matches, used by `match`
+    MatchBlock,
+
+    /// A match pattern, eg `{a: $foo}`
+    MatchPattern,
+
     /// Nothing
     Nothing,
 
@@ -137,6 +143,8 @@ impl SyntaxShape {
                 Type::List(Box::new(contents))
             }
             SyntaxShape::Keyword(_, expr) => expr.to_type(),
+            SyntaxShape::MatchBlock => Type::Any,
+            SyntaxShape::MatchPattern => Type::Any,
             SyntaxShape::MathExpression => Type::Any,
             SyntaxShape::Nothing => Type::Any,
             SyntaxShape::Number => Type::Number,
@@ -196,6 +204,8 @@ impl Display for SyntaxShape {
             SyntaxShape::Variable => write!(f, "var"),
             SyntaxShape::VarWithOptType => write!(f, "vardecl"),
             SyntaxShape::Signature => write!(f, "signature"),
+            SyntaxShape::MatchPattern => write!(f, "matchpattern"),
+            SyntaxShape::MatchBlock => write!(f, "matchblock"),
             SyntaxShape::Expression => write!(f, "expression"),
             SyntaxShape::Boolean => write!(f, "bool"),
             SyntaxShape::Error => write!(f, "error"),