Java: Add common base class for SwitchStmt and SwitchExpr

[Marcono1234]

Description of the issue
Would it be possible to add a common base class for SwitchStmt and SwitchExpr?
Currently both classes define common predicates and it is often useful to find out whether a switch covers certain values, regardless of whether it is a statement or an expression.
Common predicates:

• getACase
• getAConstCase
• getAStmt
• getDefaultCase
• getExpr
• getStmt

Some built-in QL types and queries would likely profit from this as well (though classes like ConstSwitchStmt would have to be redesigned to extend from this new class?).