[Doc] Minimum and maximum requires for targets

[kaby76]

This PR requires some version of Java newer than version 11. Antlr4 itself requires version 11 for the tool, version 8 for the runtime. There isn't a thing in the documentation about what are the minimum and maximum required versions for all the targets, which consequently restrict what can be placed in this repo.

[teverett]

Comment copied from from #2627

@kaby76 thanks for bringing this up. I've been a little concerned about it for a while. Java has moved on and even Java 11 is numerous revisions behind the current one. I agree that we need to update the docs and I also think we need to update our min java version across this repo, the formatter and the tester repos. I think first step is to update the tester:

https://github.com/antlr/antlr4test-maven-plugin

Is there a minimum java version we should be targeting?