feat(runtime): add `terminal.input` for writing to stdin

During https://github.com/stackblitz/tutorialkit/pull/348 it was noticed that terminal.write cannot be used to write into terminal's stdin. It's only useful for writing to stdout.
Adds new terminal method that can be used to write commands to stdin. The #348 will add proper example into documentation.

import tutorialStore from 'tutorialkit:store';

export default function Example() {
  async function onClick() {
    const terminal = tutorialStore.terminalConfig.value!.panels[0];
    terminal.input('npm run test\n');
  }

  return (
    <button
      onClick={onClick}
      className="px-4 py-1 my-3 cursor-pointer border-1 border-tk-border-primary rounded-md bg-tk-elements-primaryButton-backgroundColor text-tk-elements-primaryButton-textColor"
    >
      Run tests
    </button>
  );
}

stackblitz / tutorialkit

feat(runtime): add `terminal.input` for writing to stdin #350