`PartialEvaluator` could add casts to the `CtExpression`s of a `Ct(Unary|Binary)Operator` and remove redundant casts from a `CtExpression`

Each `CtExpression` has a list of casts that are applied to it. Depending on the type and context of the expression an implicit cast might be performed. This is implemented through the `OperatorHelper.getPromotedType`.

At the moment the code ignores `CtBinaryOperator` where both the left and right are unknown. One could add those casts to the `CtExpression`. For example, the expression `s` in `int a = ...; short s = 1; if (s < a) { ... }` would be promoted to `int`, so the `PartialEvaluator` could add the cast to the list of casts.

Another optimization that came to mind would be to remove unnecessary casts. I have not thought much about when a cast is unnecessary. Only duplicate casts like `(double) (double) value` came to mind. Maybe widening casts like `(int) byte`, but this could conflict with the above that adds casts to expressions.