refactoring HDLTyper/VhdlTyper to (Vhdl)TypeSystemAdapter
moved code related to generators from synflow.core to synflow.ngDesign
(vhdl) always uses shift_left/right (instead of sub-vectors)
This just complicated things for little benefit
simplified AbstractExpressionTransformer
distinct caseExpr* no longer call caseExpression
updated VhdlCastAdder to pass results to caseExpression
working on TypeSystemAdapter to remove duplicate resizes
corrected bug in type system adapter, sometimes needs to cast resize
improved comment in VHDL type system adapter