Checker does not check that all parent variables are assigned to

[JSAbrahams]

Description of Bug

Actually, this is slightly more complicated.
To implement this fully we will need to specify in the context that a variable is not assigned to in a class.
Said class is then implicitly an abstract class.
Then, it falls to any concrete implementations of the class to assign to variable.
Non-trivial since we have no abstract keyword for classes of course, so we would have to check this during each use whether the constructor assigns to all variables or not.

Expected behavior

Additional context