Services: Fix visibility of Object-derivative constructors

Derivatives of Core::Object should be constructed through
ClassName::construct(), to avoid handling ref-counted objects with
refcount zero. Fixing the visibility means that misuses like this are
more difficult.

Userland/Services/SQLServer/SQLStatement.h

@@ -18,6 +18,8 @@ namespace SQLServer {
 
 class SQLStatement final : public Core::Object {
     C_OBJECT(SQLStatement)
+
+public:
     ~SQLStatement() override = default;
 
     static RefPtr<SQLStatement> statement_for(int statement_id);