Python: Add self-validating CFG tests

These tests consist of various Python constructions (hopefully a
somewhat comprehensive set) with specific timestamp annotations
scattered throughout. When the tests are run using the Python 3
interpreter, these annotations are checked and compared to the "current
timestamp" to see that they are in agreement. This is what makes the
tests "self-validating".

There are a few different kinds of annotations: the basic `t[4]` style
(meaning this is executed at timestamp 4), the `t[dead(4)]` variant
(meaning this _would_ happen at timestamp 4, but it is in a dead
branch), and `t[never]` (meaning this is never executed at all).

In addition to this, there is a query, MissingAnnotations, which checks
whether we have applied these annotations maximally. Many expression
nodes are not actually annotatable, so there is a sizeable list of
excluded nodes for that query.

Author: tausbn

python/ql/test/library-tests/ControlFlow/evaluation-order/MissingAnnotations.expected

@@ -0,0 +1,15 @@
+/**
+ * Finds expressions in test functions that lack a timer annotation
+ * and are not part of the timer mechanism or otherwise excluded.
+ * An empty result means every annotatable expression is covered.
+ */
+
+import python
+import TimerUtils
+
+from TestFunction f, Expr e
+where
+  e.getScope().getEnclosingScope*() = f and
+  not isTimerMechanism(e, f) and
+  not isUnannotatable(e)
+select e, "Missing annotation in $@", f, f.getName()

python/ql/test/library-tests/ControlFlow/evaluation-order/MissingAnnotations.ql

@@ -0,0 +1,16 @@
+/**
+ * Implementation of the evaluation-order CFG signature using the existing
+ * Python control flow graph.
+ */
+
+private import python as Py
+import TimerUtils
+
+/** Existing Python CFG implementation of the evaluation-order signature. */
+module OldCfg implements EvalOrderCfgSig {
+  class CfgNode = Py::ControlFlowNode;
+
+  class BasicBlock = Py::BasicBlock;
+
+  CfgNode scopeGetEntryNode(Py::Scope s) { result = s.getEntryNode() }
+}