Move Value to helpers, separate span call (#10121)

# Description

As part of the refactor to split spans off of Value, this moves to using
helper functions to create values, and using `.span()` instead of
matching span out of Value directly.

Hoping to get a few more helping hands to finish this, as there are a
lot of commands to update :)

# User-Facing Changes
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# Tests + Formatting
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> **Note**
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---------

Co-authored-by: Darren Schroeder <343840+fdncred@users.noreply.github.com>
Co-authored-by: WindSoilder <windsoilder@outlook.com>

src/command.rs

@@ -384,10 +384,10 @@ impl Command for Nu {
         call: &Call,
         _input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
-        Ok(Value::String {
-            val: get_full_help(&Nu.signature(), &Nu.examples(), engine_state, stack, true),
-            span: call.head,
-        }
+        Ok(Value::string(
+            get_full_help(&Nu.signature(), &Nu.examples(), engine_state, stack, true),
+            call.head,
+        )
         .into_pipeline_data())
     }
 

src/main.rs

@@ -164,13 +164,10 @@ fn main() -> Result<()> {
         let vals: Vec<_> = include_path
             .item
             .split('\x1e') // \x1e is the record separator character (a character that is unlikely to appear in a path)
-            .map(|x| Value::String {
-                val: x.trim().to_string(),
-                span,
-            })
+            .map(|x| Value::string(x.trim().to_string(), span))
             .collect();
 
-        engine_state.add_env_var("NU_LIB_DIRS".into(), Value::List { vals, span });
+        engine_state.add_env_var("NU_LIB_DIRS".into(), Value::list(vals, span));
     }
 
     start_time = std::time::Instant::now();