Changed the declaration default access specifier to be public.

This fixes some problems with CheckIgnoredDeclsPass that ignores declarations that are not public, which .

src/AST/Declaration.cs

@@ -202,6 +202,7 @@ namespace CppSharp.AST
 
         protected Declaration()
         {
+            Access = AccessSpecifier.Public;
             IgnoreFlags = IgnoreFlags.None;
             ExcludeFromPasses = new HashSet<System.Type>();
             PreprocessedEntities = new List<PreprocessedEntity>();