Move Visibility out of Declaration.

libsolidity/ast/ASTEnums.h

@@ -34,6 +34,9 @@ namespace solidity
 // How a function can mutate the EVM state.
 enum class StateMutability { Pure, View, NonPayable, Payable };
 
+/// Visibility ordered from restricted to unrestricted.
+enum class Visibility { Default, Private, Internal, Public, External };
+
 inline std::string stateMutabilityToString(StateMutability const& _stateMutability)
 {
 	switch (_stateMutability)