Download and Install Oracle JDK 21 on macOS

Guide to setup Java Development Kit (JDK) version 21 with Oracle JDK on Mac operating system (macOS). I'll show you every step of the way:
- What is Oracle JDK?
- What is JDK version 21?
- Download DMG installer of Oracle JDK 21 for macOS
- Verify integrity of the downloaded file
- Install Oracle JDK 21 on macOS
- Verify installation by checking versions of java and javac
- Check JDK installation path