Keep source level at JDK11

[berndmoos]

In order to be able to run with JDK11 upwards which is good for debugging. Not going beyond JDK11 in the source basically means not doing this:

(if o instanceof SomeType someType){
     someType.someMethod();
}

but rather

(if o instanceof SomeType){
    SomeType someType = (SomeType)o;
     someType.someMethod();
}

And it also means not using text blocks for string initialisation

[berndmoos]

Could even go back to JDK8. Do I want to?