Use BindableStaticNameExpression not BindableStaticAccessExpression

This type does allow identifiers, but those are ruled out earlier, so I added
an assert for that case.

Author: sandersn

src/compiler/binder.ts

@@ -2983,18 +2983,16 @@ namespace ts {
                 addLateBoundAssignmentDeclarationToSymbol(node, sym);
             }
             else {
-                if (!isBindableStaticAccessExpression(node.left)) {
-                    return Debug.fail(`Invalid cast. The supplied value ${getTextOfNode(node.left)} was not a BindableStaticAccessExpression.`);
-                }
-                bindStaticPropertyAssignment(node.left as BindableStaticAccessExpression);
+                bindStaticPropertyAssignment(cast(node.left, isBindableStaticNameExpression));
             }
         }
 
         /**
          * For nodes like `x.y = z`, declare a member 'y' on 'x' if x is a function (or IIFE) or class or {}, or not declared.
          * Also works for expression statements preceded by JSDoc, like / ** @type number * / x.y;
          */
-        function bindStaticPropertyAssignment(node: BindableStaticAccessExpression) {
+        function bindStaticPropertyAssignment(node: BindableStaticNameExpression) {
+            Debug.assert(!isIdentifier(node));
             node.expression.parent = node;
             bindPropertyAssignment(node.expression, node, /*isPrototypeProperty*/ false, /*containerIsClass*/ false);
         }