C++: Fix special-casing of Qt library

The `Expr.getType` predicate returns a pointer type since that's the
type of the `new`-expression as a whole. To find the class type, we use
`NewExpr.getAllocatedType`.

This commit reduces the number of alerts in a Qt snapshot from 229 to
51, and it removes the two false positives in
https://github.com/Subsurface-divelog/subsurface.

Author: jbj

cpp/ql/src/jsf/4.10 Classes/AV Rule 79.ql

@@ -267,7 +267,7 @@ predicate automaticallyReleased(Assignment acquire)
 {
   // sub-types of the Qt type QObject are released by their parent (if they have one)
   exists(NewExpr alloc |
-    alloc.getType() = qtObject() and
+    alloc.getAllocatedType() = qtObject() and
     acquire.getRValue() = alloc and
     alloc.getInitializer() = qtParentConstructor().getACallToThisFunction()
   )

cpp/ql/test/query-tests/jsf/4.10 Classes/AV Rule 79/AV Rule 79.expected

@@ -14,9 +14,6 @@
 | ListDelete.cpp:21:3:21:21 | ... = ... | Resource first is acquired by class MyThingColection but not released anywhere in this class. |
 | NoDestructor.cpp:23:3:23:20 | ... = ... | Resource n is acquired by class MyClass5 but not released anywhere in this class. |
 | PlacementNew.cpp:36:3:36:36 | ... = ... | Resource p1 is acquired by class MyTestForPlacementNew but not released anywhere in this class. |
-| QObject.cpp:16:5:16:46 | ... = ... | Resource noParent is acquired by class MyQtUser but not released anywhere in this class. |
-| QObject.cpp:20:5:20:54 | ... = ... | Resource constructorParent is acquired by class MyQtUser but not released anywhere in this class. |
-| QObject.cpp:22:5:22:49 | ... = ... | Resource laterParent is acquired by class MyQtUser but not released anywhere in this class. |
 | SelfRegistering.cpp:25:3:25:24 | ... = ... | Resource side is acquired by class MyOwner but not released anywhere in this class. |
 | Variants.cpp:25:3:25:13 | ... = ... | Resource f is acquired by class MyClass4 but not released anywhere in this class. |
 | Variants.cpp:65:3:65:17 | ... = ... | Resource a is acquired by class MyClass6 but not released anywhere in this class. |

cpp/ql/test/query-tests/jsf/4.10 Classes/AV Rule 79/QObject.cpp

@@ -13,13 +13,13 @@ class MyQtUser {
   MyQtUser(QObject *parent) {
     // This object sets its parent pointer to null and thus must be deleted
     // manually.
-    noParent = new DerivedFromQObject(nullptr); // BAD
+    noParent = new DerivedFromQObject(nullptr); // BAD [NOT DETECTED]
 
     // This object does not need to be deleted because it will be deleted by
     // its parent object when the time is right.
-    constructorParent = new DerivedFromQObject(parent); // GOOD [FALSE POSITIVE]
+    constructorParent = new DerivedFromQObject(parent); // GOOD
 
-    laterParent = new DerivedFromQObject(nullptr); // GOOD [FALSE POSITIVE]
+    laterParent = new DerivedFromQObject(nullptr); // GOOD
     laterParent->setParent(parent);
   }
 };