Add helper method to check whether ctrl+c was pressed, adopt it (#7482)

I've been working on streaming and pipeline interruption lately. It was
bothering me that checking ctrl+c (something we want to do often) always
requires a bunch of boilerplate like:
```rust
use std::sync::atomic::Ordering;

if let Some(ctrlc) = &engine_state.ctrlc {
     if ctrlc.load(Ordering::SeqCst) {
          ...
```
I added a helper method to cut that down to:

```rust
if nu_utils::ctrl_c::was_pressed(&engine_state.ctrlc) {
    ...
```

crates/nu-protocol/src/value/stream.rs

@@ -1,10 +1,7 @@
 use crate::*;
 use std::{
     fmt::Debug,
-    sync::{
-        atomic::{AtomicBool, Ordering},
-        Arc,
-    },
+    sync::{atomic::AtomicBool, Arc},
 };
 
 pub struct RawStream {
@@ -77,10 +74,8 @@ impl Iterator for RawStream {
     type Item = Result<Value, ShellError>;
 
     fn next(&mut self) -> Option<Self::Item> {
-        if let Some(ctrlc) = &self.ctrlc {
-            if ctrlc.load(Ordering::SeqCst) {
-                return None;
-            }
+        if nu_utils::ctrl_c::was_pressed(&self.ctrlc) {
+            return None;
         }
 
         // If we know we're already binary, just output that
@@ -223,12 +218,8 @@ impl Iterator for ListStream {
     type Item = Value;
 
     fn next(&mut self) -> Option<Self::Item> {
-        if let Some(ctrlc) = &self.ctrlc {
-            if ctrlc.load(Ordering::SeqCst) {
-                None
-            } else {
-                self.stream.next()
-            }
+        if nu_utils::ctrl_c::was_pressed(&self.ctrlc) {
+            None
         } else {
             self.stream.next()
         }