Editorial: Define Evaluation for BindingIdentifier

PR tc39#614 defined (in Annex B) an additional form for ForInOfStatement.
Performing ForInOfLoopEvaluation on it ends with a call to ForIn/OfBodyEvaluation,
with |BindingIdentifier| as first arg, passed to the _lhs_ param.
ForIn/OfBodyEvaluation (at step 6.g.i.1) evaluates this param,
but there's no definition of Evaluation for |BindingIdentifier|.
This PR adds the necessary definition.

(The new definition basically just duplicates the one for ForBinding.
In fact, if this part of Annex B is merged into the main spec,
the definition for ForBinding can be dropped,
since it can just chain to this new definition.)

spec.html

@@ -42064,6 +42064,17 @@ <h1>Initializers in ForIn Statement Heads</h1>
         1. Let _keyResult_ be ? ForIn/OfHeadEvaluation(&laquo; &raquo;, |Expression|, ~enumerate~).
         1. Return ? ForIn/OfBodyEvaluation(|BindingIdentifier|, |Statement|, _keyResult_, ~enumerate~, ~varBinding~, _labelSet_).
       </emu-alg>
+      <p>The runtime semantics of Evaluation are augmented with the following:</p>
+      <emu-grammar>
+        BindingIdentifier :
+          Identifier
+          `yield`
+          `await`
+      </emu-grammar>
+      <emu-alg>
+        1. Let _bindingId_ be StringValue of |BindingIdentifier|.
+        1. Return ? ResolveBinding(_bindingId_).
+      </emu-alg>
     </emu-annex>
 
     <emu-annex id="sec-IsHTMLDDA-internal-slot">