New commands: break, continue, return, and loop (#7230)

# Description

This adds `break`, `continue`, `return`, and `loop`.

* `break` - breaks out a loop
* `continue` - continues a loop at the next iteration
* `return` - early return from a function call
* `loop` - loop forever (until the loop hits a break)

Examples:
```
for i in 1..10 {
    if $i == 5 {
       continue
    } 
    print $i
}
```

```
for i in 1..10 {
    if $i == 5 {
        break
    } 
    print $i
}
```

```
def foo [x] {
    if true {
        return 2
    }
    $x
}
foo 100
```

```
loop { print "hello, forever" }
```

```
[1, 2, 3, 4, 5] | each {|x| 
    if $x > 3 { break }
    $x
}
```

# User-Facing Changes

Adds the above commands.

# 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-engine/src/eval.rs

@@ -156,7 +156,7 @@ pub fn eval_call(
             }
         }
 
-        let result = eval_block(
+        let result = eval_block_with_early_return(
             engine_state,
             &mut callee_stack,
             block,
@@ -944,6 +944,27 @@ pub fn eval_element_with_input(
     }
 }
 
+pub fn eval_block_with_early_return(
+    engine_state: &EngineState,
+    stack: &mut Stack,
+    block: &Block,
+    input: PipelineData,
+    redirect_stdout: bool,
+    redirect_stderr: bool,
+) -> Result<PipelineData, ShellError> {
+    match eval_block(
+        engine_state,
+        stack,
+        block,
+        input,
+        redirect_stdout,
+        redirect_stderr,
+    ) {
+        Err(ShellError::Return(_, value)) => Ok(PipelineData::Value(*value, None)),
+        x => x,
+    }
+}
+
 pub fn eval_block(
     engine_state: &EngineState,
     stack: &mut Stack,

crates/nu-engine/src/lib.rs

@@ -11,7 +11,7 @@ pub use column::get_columns;
 pub use documentation::get_full_help;
 pub use env::*;
 pub use eval::{
-    eval_block, eval_call, eval_expression, eval_expression_with_input, eval_operator,
-    eval_subexpression, eval_variable, redirect_env,
+    eval_block, eval_block_with_early_return, eval_call, eval_expression,
+    eval_expression_with_input, eval_operator, eval_subexpression, eval_variable, redirect_env,
 };
 pub use glob_from::glob_from;