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

[AriPerkkio]

• During docs: add example of tutorialkit:store and tutorialkit:core usages #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 docs: add example of tutorialkit:store and tutorialkit:core usages #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]

Run & review this pull request in StackBlitz Codeflow.

[Nemikolh]

Looks good! Glad we found and fixed that bug! 🤩