JavaScript: Back out parsing of qualified XML identifiers.

Their syntax conflicts with the proposed function-bind operator, which is more important to support.

javascript/ql/test/query-tests/Declarations/UnusedVariable/funbind.js

@@ -0,0 +1,6 @@
+function test(bar, e) {
+  let foo = bar;
+  e.target::foo::baz();
+}
+
+// semmle-extractor-options: --experimental