Use wildcards for least upper bound of two lists

[MeAmAnUsername]

Summary
Use a list of upperbounded wildcard as least upper bound for two lists: val res: (_ <: Fruit)* = if(flag) apples else bananas

Todo

• Write tests
  • At least one test for where the resulting element type is the top type
• Implement

Reason
It currently uses a list of toptype, but that is less precise than a list of an upperbounded wildcard. It may actually be incorrect too It is also incorrect: if(true) [0] else ["zero"] generates invalid Java code, as it tries to make the assignment ArrayList<Object> obj = ArrayList<Integer>

Description
In case the least upper bound of the element types is toptype, just use a list of toptype (as it does now) instead of a list of a wildcard upperbounded by toptype, if that is possible (see possible incorrectness in reason above). just use a list of wildcards instead: ArrayList<?>

Implementation
Least upper bound of X* and Y* becomes (_ <: lub(X, Y))*, unless lub(X, Y) == TopType(), then it becomes (_)*

Related issues
None?