readline: prompt opt-out behavior

* **Version**: v8.0.0-rc.0 * **Platform**: Windows 4 x64 * **Subsystem**: readline I am not sure if this is a bug or a feature. Consider this simple echo interface: ```js 'use strict'; const readline = require('readline'); const rl = readline.createInterface({ input: process.stdin, output: process.stdout, }); rl.on('line', (line) => { console.log(line); }); ``` It does not use `rl.prompt()` anywhere and with a common input there will be no default prompt: <details> <summary>GIF 1:</summary>  </details><br> However, if a user press DELETE, BACKSPACE or UP button, default prompt immediately and somehow unexpectedly appears shifting the whole line: <details> <summary>GIF 2:</summary>  </details><br> This can be prevented by setting the `prompt` option into the empty line. However, I am not sure if this opt-out rule is an intended behavior.