Scala 2 differs from 3 with forward declarations

[marcusklang]

{
   val b = a;
   val a = 42;
}

Compiles and works, but in Scala 2 you were given a warning. In Scala 3 you are not given a warning.

b is given the value 0.

Update compendium answers for exercise 4.2 to reflect changes.

[bjornregnell]

https://docs.scala-lang.org/scala3/reference/other-new-features/safe-initialization.html

[bjornregnell]

https://github.com/lampepfl/dotty/issues/16083