C++: Expose is_structured_binding as a member of Variable

Author: jketema

cpp/ql/lib/semmle/code/cpp/Variable.qll

@@ -169,6 +169,12 @@ class Variable extends Declaration, @variable {
     variable_instantiation(underlyingElement(this), unresolveElement(v))
   }
 
+  /**
+   * Holds if this variable is declated as part of a structured binding
+   * declaration. For example, `x` in `auto [x, y] = ...`.
+   */
+  predicate isStructuredBinding() { is_structured_binding(unresolveElement(this)) }
+
   /**
    * Holds if this is a compiler-generated variable. For example, a
    * [range-based for loop](http://en.cppreference.com/w/cpp/language/range-for)