Update checking of bounds declarations to handle lexically-hidden variables

[dtarditi]

We dropped the requirement that variables not be lexically hidden. We need to add some additional conditions about checking of bounds declarations involving lexically hidden variables. For example, we might need to add a condition that variables are suitably renamed before checking so that there is no lexical hiding, or something equivalent to that.

In a compiler implementation, this all drops out because the compiler will internally distinguish between variables in different scopes with the same name.