Java: Fix support for variable capture inside object initializers.

java/ql/lib/semmle/code/java/dataflow/internal/DataFlowPrivate.qll

@@ -147,7 +147,14 @@ private module CaptureInput implements VariableCapture::InputSig<Location> {
   }
 
   class Callable extends J::Callable {
-    predicate isConstructor() { this instanceof Constructor }
+    predicate isConstructor() {
+      // InstanceInitializers are called from constructors and are equally likely
+      // to capture variables for the purpose of field initialization, so we treat
+      // them as constructors for the heuristic identification of whether to allow
+      // this-to-this summaries.
+      this instanceof Constructor or
+      this instanceof InstanceInitializer
+    }
   }
 }