Java: Add TypeFlow base case for partially unbound types.

Author: aschackmull

java/ql/lib/semmle/code/java/dataflow/TypeFlow.qll

@@ -202,6 +202,13 @@ private module Input implements TypeFlowInput<Location> {
       t1e = t2e and
       unbound(t2) and
       not unbound(t1)
+      or
+      t1e = t2e and
+      exists(int pos |
+        partiallyUnbound(t2, pos) and
+        not partiallyUnbound(t1, pos) and
+        not unbound(t1)
+      )
     )
   }
 
@@ -370,6 +377,11 @@ private module Input implements TypeFlowInput<Location> {
     )
   }
 
+  /** Holds if `t` is a parameterised type with unrestricted type argument at position `pos`. */
+  private predicate partiallyUnbound(ParameterizedType t, int pos) {
+    unconstrained(t.getTypeArgument(pos))
+  }
+
   Type getErasure(Type t) { result = t.getErasure() }
 
   Type getAnAncestor(Type sub) { result = sub.getAnAncestor() }