feat(Escaped Identifiers): add ability to use any symbol wrapped in back ticks.

js/js.translator/testData/box/escapedIdentifiers/externalEscapedTopLevel.js

@@ -0,0 +1,9 @@
+this["@get something-invalid"] = function() {
+    return "something invalid"
+}
+
+this["some+value"] = 42
+
+this["+some+object%:"] = {
+    foo: "%%++%%"
+}