C++: Make constructor-used-as-copy-constructor warning/low

This query is supposed to look for constructors that unintentionally qualify as copy constructors due to default arguments. There are quite a few real-world projects that define such constructors intentionally. I've reduced the severity to "warning" and the precision to "low" due to the high false positive rate.

Author: dave-bartolomeo

cpp/ql/src/jsf/4.10 Classes/AV Rule 77.1.qhelp

@@ -11,8 +11,7 @@ when their default arguments are taken into account. An example would be a const
 of the form <code>X(const X&amp; rhs, int i = 0)</code>. A compiler will use such a constructor as a copy
 constructor in preference to the default member-wise copy constructor that it would otherwise generate.
 Since this is usually not what was intended, constructors of the form often do not provide the right
-semantics for copying objects of the class, making them potentially dangerous. Even when this sort of
-thing has been done intentionally, it is confusing and in bad taste, and should be avoided.
+semantics for copying objects of the class, making them potentially dangerous.
 </p>
 
 </overview>

cpp/ql/src/jsf/4.10 Classes/AV Rule 77.1.ql

@@ -2,8 +2,8 @@
  * @name Constructor with default arguments will be used as a copy constructor
  * @description Constructors with default arguments should not be signature-compatible with a copy constructor when their default arguments are taken into account.
  * @kind problem
- * @problem.severity error
- * @precision high
+ * @problem.severity warning
+ * @precision low
  * @id cpp/constructor-used-as-copy-constructor
  * @tags reliability
  *       readability