add a new LoadStoreStep as a StepSummary for TypeTracking

javascript/ql/src/semmle/javascript/dataflow/TypeTracking.qll

@@ -44,7 +44,7 @@ private newtype TTypeTracker = MkTypeTracker(Boolean hasCall, OptionalPropertyNa
  */
 class TypeTracker extends TTypeTracker {
   Boolean hasCall;
-  string prop;
+  OptionalPropertyName prop;
 
   TypeTracker() { this = MkTypeTracker(hasCall, prop) }
 
@@ -53,6 +53,8 @@ class TypeTracker extends TTypeTracker {
   TypeTracker append(StepSummary step) {
     step = LevelStep() and result = this
     or
+    step = LoadStoreStep(prop) and result = this
+    or
     step = CallStep() and result = MkTypeTracker(true, prop)
     or
     step = ReturnStep() and hasCall = false and result = this
@@ -211,6 +213,8 @@ class TypeBackTracker extends TTypeBackTracker {
   TypeBackTracker prepend(StepSummary step) {
     step = LevelStep() and result = this
     or
+    step = LoadStoreStep(prop) and result = this
+    or
     step = CallStep() and hasReturn = false and result = this
     or
     step = ReturnStep() and result = MkTypeBackTracker(true, prop)

javascript/ql/src/semmle/javascript/dataflow/internal/StepSummary.qll

@@ -34,7 +34,8 @@ newtype TStepSummary =
   CallStep() or
   ReturnStep() or
   StoreStep(PropertyName prop) or
-  LoadStep(PropertyName prop)
+  LoadStep(PropertyName prop) or
+  LoadStoreStep(PropertyName prop)
 
 /**
  * INTERNAL: Use `TypeTracker` or `TypeBackTracker` instead.
@@ -53,6 +54,8 @@ class StepSummary extends TStepSummary {
     exists(string prop | this = StoreStep(prop) | result = "store " + prop)
     or
     exists(string prop | this = LoadStep(prop) | result = "load " + prop)
+    or
+    exists(string prop | this = LoadStoreStep(prop) | result = "in " + prop)
   }
 }