Python: Add AnnAssign DefinitionNode

This was a source of false positives for the
`py/uninitialized-local-variable` query, as exemplified by the test
case.

Author: tausbn

python/ql/src/semmle/python/Flow.qll

@@ -653,6 +653,8 @@ class DefinitionNode extends ControlFlowNode {
   DefinitionNode() {
     exists(Assign a | a.getATarget().getAFlowNode() = this)
     or
+    exists(AnnAssign a | a.getTarget().getAFlowNode() = this and exists(a.getValue()))
+    or
     exists(Alias a | a.getAsname().getAFlowNode() = this)
     or
     augstore(_, this)
@@ -795,6 +797,9 @@ private AstNode assigned_value(Expr lhs) {
   /* lhs = result */
   exists(Assign a | a.getATarget() = lhs and result = a.getValue())
   or
+  /* lhs : annotation = result */
+  exists(AnnAssign a | a.getTarget() = lhs and result = a.getValue())
+  or
   /* import result as lhs */
   exists(Alias a | a.getAsname() = lhs and result = a.getValue())
   or

python/ql/test/query-tests/Variables/undefined/UninitializedLocal.expected

@@ -11,5 +11,4 @@
 | UninitializedLocal.py:163:7:163:7 | x | Local variable 'x' may be used before it is initialized. |
 | UninitializedLocal.py:176:16:176:16 | x | Local variable 'x' may be used before it is initialized. |
 | UninitializedLocal.py:178:16:178:16 | y | Local variable 'y' may be used before it is initialized. |
-| UninitializedLocal.py:294:14:294:22 | annotated | Local variable 'annotated' may be used before it is initialized. |
 | odasa3987.py:11:8:11:10 | var | Local variable 'var' may be used before it is initialized. |