Python: Remove points-to to from ControlFlowNode

Moves the existing points-to predicates to the newly added class
`ControlFlowNodeWithPointsTo` which resides in the `LegacyPointsTo`
module.

(Existing code that uses these predicates should import this module, and
references to `ControlFlowNode` should be changed to
`ControlFlowNodeWithPointsTo`.)

Also updates all existing points-to based code to do just this.

python/ql/test/2/library-tests/PointsTo/class_properties/ClassValues.ql

@@ -1,10 +1,11 @@
 import python
+private import LegacyPointsTo
 
 from ClassValue cls, string res
 where
   exists(CallNode call |
     call.getFunction().(NameNode).getId() = "test" and
-    call.getAnArg().pointsTo(cls)
+    call.getAnArg().(ControlFlowNodeWithPointsTo).pointsTo(cls)
   ) and
   (
     cls.isSequence() and

python/ql/test/2/library-tests/PointsTo/imports/Runtime.ql

@@ -1,6 +1,7 @@
 import python
+private import LegacyPointsTo
 
-from int line, ControlFlowNode f, Object o, ControlFlowNode orig
+from int line, ControlFlowNodeWithPointsTo f, Object o, ControlFlowNode orig
 where
   not f.getLocation().getFile().inStdlib() and
   f.refersTo(o, orig) and

python/ql/test/2/library-tests/PointsTo/imports2/Runtime.ql

@@ -1,6 +1,7 @@
 import python
+private import LegacyPointsTo
 
-from int line, ControlFlowNode f, Object o, ControlFlowNode orig
+from int line, ControlFlowNodeWithPointsTo f, Object o, ControlFlowNode orig
 where
   not f.getLocation().getFile().inStdlib() and
   f.refersTo(o, orig) and

python/ql/test/2/library-tests/PointsTo/imports2/RuntimeWithType.ql

@@ -1,6 +1,7 @@
 import python
+private import LegacyPointsTo
 
-from int line, ControlFlowNode f, Object o, ClassObject cls, ControlFlowNode orig
+from int line, ControlFlowNodeWithPointsTo f, Object o, ClassObject cls, ControlFlowNode orig
 where
   not f.getLocation().getFile().inStdlib() and
   f.refersTo(o, cls, orig) and

python/ql/test/2/library-tests/PointsTo/origin_uniqueness/Origin.ql

@@ -1,8 +1,9 @@
 import python
+private import LegacyPointsTo
 
 string short_loc(Location l) { result = l.getFile().getShortName() + ":" + l.getStartLine() }
 
-from ControlFlowNode use, Object obj, ControlFlowNode orig, int line
+from ControlFlowNodeWithPointsTo use, Object obj, ControlFlowNode orig, int line
 where
   use.refersTo(obj, orig) and
   use.getLocation().getFile().getShortName() = "test.py" and