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_plugin_example/src/commands/collect_bytes.rs

@@ -1,7 +1,7 @@
 use nu_plugin::{EngineInterface, EvaluatedCall, PluginCommand};
 use nu_protocol::{
-    ByteStream, ByteStreamType, Category, Example, LabeledError, PipelineData, Signature, Type,
-    Value,
+    ByteStream, ByteStreamType, Category, Example, LabeledError, PipelineData, Signals, Signature,
+    Type, Value,
 };
 
 use crate::ExamplePlugin;
@@ -52,7 +52,7 @@ impl PluginCommand for CollectBytes {
             ByteStream::from_result_iter(
                 input.into_iter().map(Value::coerce_into_binary),
                 call.head,
-                None,
+                Signals::empty(),
                 ByteStreamType::Unknown,
             ),
             None,

crates/nu_plugin_example/src/commands/generate.rs

@@ -1,7 +1,7 @@
 use nu_plugin::{EngineInterface, EvaluatedCall, PluginCommand};
 use nu_protocol::{
-    Category, Example, IntoInterruptiblePipelineData, LabeledError, PipelineData, Signature,
-    SyntaxShape, Type, Value,
+    Category, Example, IntoInterruptiblePipelineData, LabeledError, PipelineData, Signals,
+    Signature, SyntaxShape, Type, Value,
 };
 
 use crate::ExamplePlugin;
@@ -85,7 +85,7 @@ impl PluginCommand for Generate {
                 })
                 .map(|result| result.unwrap_or_else(|err| Value::error(err, head)))
         })
-        .into_pipeline_data(head, None))
+        .into_pipeline_data(head, Signals::empty()))
     }
 }
 

crates/nu_plugin_example/src/commands/seq.rs

@@ -1,6 +1,7 @@
 use nu_plugin::{EngineInterface, EvaluatedCall, PluginCommand};
 use nu_protocol::{
-    Category, Example, LabeledError, ListStream, PipelineData, Signature, SyntaxShape, Type, Value,
+    Category, Example, LabeledError, ListStream, PipelineData, Signals, Signature, SyntaxShape,
+    Type, Value,
 };
 
 use crate::ExamplePlugin;
@@ -54,7 +55,7 @@ impl PluginCommand for Seq {
         let first: i64 = call.req(0)?;
         let last: i64 = call.req(1)?;
         let iter = (first..=last).map(move |number| Value::int(number, head));
-        Ok(ListStream::new(iter, head, None).into())
+        Ok(ListStream::new(iter, head, Signals::empty()).into())
     }
 }