DVB Inspector 1.20 will require java 21

[EricBerendsen]

Early warning; the next release of DVB Inspector (1.20) will require Java 21. I know this may inconvenience some users, as some people may not have the admin rights to install a new version of Java, or Java 21 may not yet be available for their OS

One reason is that oracle is no longer releasing free updates to Java 17

The other reason is I want to play with new features of Java 21. I have two main goals when working on DVB Inspector; learning about DVB and learning about new features of Java. I think there are enough new features in Java 21 to justify upgrading to this new version.