Added DeclarationCompleter to compute actual/refinedDeclaration lazily for ceylon/ceylon-compiler#1631
ExpressionVisitor: add actual/shared annotations to the model of shortcut refined members

This way they are in line with manual declarations
Util: remove Array from overloading computations, as interop does not use c.l.Array for variadic methods
ModuleValidator: don't traverse the language module dependencies unless we're compiling it ceylon/ceylon-compiler#1631