JS: Fix extraction of identifiers in EXPORT_BASE context

This is needed to ensure that the base of the RHS of an ImportEqualsDeclaration is bound to a namespace. That is, B below should be bound to a namespace:

import A = B.C.D;

javascript/ql/test/library-tests/TypeScript/RegressionTests/ExportBaseResolution/test.expected

@@ -1 +1,2 @@
+| A | namespace | test.d.ts:1:19:1:19 | A | test.d.ts:10:14:10:14 | A |
 | A | variable | test.d.ts:1:19:1:19 | A | test.d.ts:10:14:10:14 | A |