C++: Fix NameQualifyingElement db inconsistency

Author: jketema

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

@@ -1071,7 +1071,7 @@ class NullPointerType extends BuiltInType {
  * const float fa[40];
  * ```
  */
-class DerivedType extends Type, @derivedtype {
+class DerivedType extends Type, NameQualifyingElement, @derivedtype {
   override string toString() { result = this.getName() }
 
   override string getName() { derivedtypes(underlyingElement(this), result, _, _) }

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -1430,7 +1430,8 @@ specialnamequalifyingelements(
 @namequalifyingelement = @namespace
                        | @specialnamequalifyingelement
                        | @usertype
-                       | @decltype;
+                       | @decltype
+                       | @derivedtype;
 
 namequalifiers(
     unique int id: @namequalifier,

cpp/ql/test/library-tests/name_qualifiers/DB-CHECK.expected

@@ -1,5 +1,5 @@
 | inconsistency2.cpp:3:3:3:5 | T:: | inconsistency2.cpp:3:3:3:6 | x | inconsistency2.cpp:2:20:2:20 | T |
-| inconsistency2.cpp:3:3:3:11 | (no string representation) | inconsistency2.cpp:3:3:3:6 | x | file://:0:0:0:0 | const s |
+| inconsistency2.cpp:3:3:3:11 | const s:: | inconsistency2.cpp:3:3:3:6 | x | file://:0:0:0:0 | const s |
 | inconsistency.cpp:7:20:7:22 | S:: | inconsistency.cpp:7:20:7:23 | (int)... | inconsistency.cpp:4:8:4:8 | S |
 | inconsistency.cpp:7:20:7:22 | S:: | inconsistency.cpp:7:20:7:23 | A | inconsistency.cpp:4:8:4:8 | S |
 | name_qualifiers.cpp:29:7:29:8 | :: | name_qualifiers.cpp:29:7:29:9 | x | file://:0:0:0:0 | (global namespace) |