Reduce likelihood of races between stdout and cooked stdin reads

[lhecker]

As explained in the comment on _getViewportCursorPosition, printing
to stdout after initiating a cooked stdin reads is a race condition
between the application and the terminal. But we can significantly
reduce the likelihood of this being obvious with this change.

Related to #18265
Possibly related to #18081

Validation Steps Performed

Execute the following Go code and start typing:

package main

import (
	"fmt"
	"time"
)

func main() {
	go func() {
		time.Sleep(50 * time.Millisecond)
		fmt.Printf("Here is a prompt! >")
	}()

	var text string
	fmt.Scanln(&text)
}

Without this change the prompt will disappear,
and with this change in place, it'll work as expected. ✅