add -e flag to print, to print the value to stderr (#5935)

* Refactor: make stdout write all and flush as generic function

* support print to stderr

crates/nu-cli/src/print.rs

@@ -21,6 +21,7 @@ impl Command for Print {
                 "print without inserting a newline for the line ending",
                 Some('n'),
             )
+            .switch("stderr", "print to stderr instead of stdout", Some('e'))
             .category(Category::Strings)
     }
 
@@ -48,11 +49,12 @@ Since this command has no output, there is no point in piping it with other comm
     ) -> Result<PipelineData, ShellError> {
         let args: Vec<Value> = call.rest(engine_state, stack, 0)?;
         let no_newline = call.has_flag("no-newline");
+        let to_stderr = call.has_flag("stderr");
         let head = call.head;
 
         for arg in args {
             arg.into_pipeline_data()
-                .print(engine_state, stack, no_newline)?;
+                .print(engine_state, stack, no_newline, to_stderr)?;
         }
 
         Ok(PipelineData::new(head))

crates/nu-cli/src/util.rs

@@ -247,7 +247,7 @@ pub fn eval_source(
                 set_last_exit_code(stack, 0);
             }
 
-            if let Err(err) = pipeline_data.print(engine_state, stack, false) {
+            if let Err(err) = pipeline_data.print(engine_state, stack, false, false) {
                 let working_set = StateWorkingSet::new(engine_state);
 
                 report_error(&working_set, &err);