feat: enable pausing handling keystrokes in watch mode

[szymonrybczak]

Summary:

In this PR I created KeyPressHandler that allows us to pause handling keystrokes because in nearest future we will add interactive prompts to start command, so they will run in watch mode. If we do not pause the handling keystrokes, the "focus" will be on the prompt. I created a function that wraps prompts and pauses and resumes interactivity in watchMode.

Test Plan:

1. Clone the repository and do all the required steps from the Contributing guide
2. Run this command:

node /path/to/react-native-cli/packages/cli/build/bin.js start

3. Press key that we're handling (a, i, d, r) and check if keystrokes are properly handled.

Checklist

• Documentation is up to date to reflect these changes.
• Follows commit message convention described in CONTRIBUTING.md

[thymikee]

small nits and this is good to go