Fix #11660: wrong reports that block-scoped variable used before its … (#11692)

* Fix #11660: wrong reports that block-scoped variable used before its declaration

* Fix code style in checker.ts

* Add unit test for #11660

* Fix the unit test for #11660

tests/cases/compiler/useBeforeDeclaration.ts

@@ -0,0 +1,20 @@
+// @outFile: test.js
+
+// @fileName: A.ts
+namespace ts {
+    export function printVersion():void {
+        log("Version: " + sys.version);  // the call of sys.version is deferred, should not report an error.
+    }
+
+    export function log(info:string):void {
+
+    }
+}
+
+// @fileName: B.ts
+namespace ts {
+
+    export let sys:{version:string} = {version: "2.0.5"};
+
+}
+