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-command/src/filesystem/watch.rs

@@ -1,5 +1,4 @@
 use std::path::PathBuf;
-use std::sync::atomic::Ordering;
 use std::sync::mpsc::{channel, RecvTimeoutError};
 use std::time::Duration;
 
@@ -252,10 +251,8 @@ impl Command for Watch {
                 }
                 Err(RecvTimeoutError::Timeout) => {}
             }
-            if let Some(ctrlc) = ctrlc_ref {
-                if ctrlc.load(Ordering::SeqCst) {
-                    break;
-                }
+            if nu_utils::ctrl_c::was_pressed(ctrlc_ref) {
+                break;
             }
         }