Add and use new Signals struct (#13314)

# Description
This PR introduces a new `Signals` struct to replace our adhoc passing
around of `ctrlc: Option<Arc<AtomicBool>>`. Doing so has a few benefits:
- We can better enforce when/where resetting or triggering an interrupt
is allowed.
- Consolidates `nu_utils::ctrl_c::was_pressed` and other ad-hoc
re-implementations into a single place: `Signals::check`.
- This allows us to add other types of signals later if we want. E.g.,
exiting or suspension.
- Similarly, we can more easily change the underlying implementation if
we need to in the future.
- Places that used to have a `ctrlc` of `None` now use
`Signals::empty()`, so we can double check these usages for correctness
in the future.

crates/nu-cmd-lang/src/core_commands/for_.rs

@@ -1,5 +1,5 @@
 use nu_engine::{command_prelude::*, get_eval_block, get_eval_expression};
-use nu_protocol::engine::CommandType;
+use nu_protocol::{engine::CommandType, Signals};
 
 #[derive(Clone)]
 pub struct For;
@@ -72,7 +72,6 @@ impl Command for For {
 
         let value = eval_expression(engine_state, stack, keyword_expr)?;
 
-        let ctrlc = engine_state.ctrlc.clone();
         let engine_state = engine_state.clone();
         let block = engine_state.get_block(block_id);
 
@@ -82,9 +81,7 @@ impl Command for For {
         match value {
             Value::List { vals, .. } => {
                 for x in vals.into_iter() {
-                    if nu_utils::ctrl_c::was_pressed(&ctrlc) {
-                        break;
-                    }
+                    engine_state.signals().check(head)?;
 
                     // with_env() is used here to ensure that each iteration uses
                     // a different set of environment variables.
@@ -116,7 +113,8 @@ impl Command for For {
                 }
             }
             Value::Range { val, .. } => {
-                for x in val.into_range_iter(span, ctrlc) {
+                for x in val.into_range_iter(span, Signals::empty()) {
+                    engine_state.signals().check(head)?;
                     stack.add_var(var_id, x);
 
                     match eval_block(&engine_state, stack, block, PipelineData::empty()) {

crates/nu-cmd-lang/src/core_commands/loop_.rs

@@ -37,6 +37,7 @@ impl Command for Loop {
         call: &Call,
         _input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
+        let head = call.head;
         let block_id = call
             .positional_nth(0)
             .expect("checked through parser")
@@ -49,9 +50,7 @@ impl Command for Loop {
         let stack = &mut stack.push_redirection(None, None);
 
         loop {
-            if nu_utils::ctrl_c::was_pressed(&engine_state.ctrlc) {
-                break;
-            }
+            engine_state.signals().check(head)?;
 
             match eval_block(engine_state, stack, block, PipelineData::empty()) {
                 Err(ShellError::Break { .. }) => {

crates/nu-cmd-lang/src/core_commands/while_.rs

@@ -46,6 +46,7 @@ impl Command for While {
         call: &Call,
         _input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
+        let head = call.head;
         let cond = call.positional_nth(0).expect("checked through parser");
         let block_id = call
             .positional_nth(1)
@@ -59,9 +60,7 @@ impl Command for While {
         let stack = &mut stack.push_redirection(None, None);
 
         loop {
-            if nu_utils::ctrl_c::was_pressed(&engine_state.ctrlc) {
-                break;
-            }
+            engine_state.signals().check(head)?;
 
             let result = eval_expression(engine_state, stack, cond)?;