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 :)

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---------

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

crates/nu-command/src/formats/to/command.rs

@@ -32,16 +32,16 @@ impl Command for To {
         call: &Call,
         _input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
-        Ok(Value::String {
-            val: get_full_help(
+        Ok(Value::string(
+            get_full_help(
                 &To.signature(),
                 &To.examples(),
                 engine_state,
                 stack,
                 self.is_parser_keyword(),
             ),
-            span: call.head,
-        }
+            call.head,
+        )
         .into_pipeline_data())
     }
 }