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-utils/src/ctrl_c.rs

@@ -0,0 +1,13 @@
+use std::sync::{
+    atomic::{AtomicBool, Ordering},
+    Arc,
+};
+
+/// Returns true if Nu has received a SIGINT signal / ctrl+c event
+pub fn was_pressed(ctrlc: &Option<Arc<AtomicBool>>) -> bool {
+    if let Some(ctrlc) = ctrlc {
+        ctrlc.load(Ordering::SeqCst)
+    } else {
+        false
+    }
+}

crates/nu-utils/src/lib.rs

@@ -1,7 +1,9 @@
+pub mod ctrl_c;
 mod deansi;
 pub mod locale;
 pub mod utils;
 
+pub use ctrl_c::was_pressed;
 pub use locale::get_system_locale;
 pub use utils::{
     enable_vt_processing, get_default_config, get_default_env, get_ls_colors,