Leave only 3*2 = 6 classes: KProperty0, KProperty1, KProperty2 and their mutable analogs, depending on the number of receivers a property takes
- move some of boxWithStdlib tests under fullJdk/ directory, where they will be compiled against the full JDK - introduce FULL_JDK in-text directive for the reflection test as only 4 tests out of 654 needed the full JDK