Prevent circular imports in ts code (#576)

js/libdeno.ts

@@ -0,0 +1,18 @@
+import { RawSourceMap } from "./types";
+import { globalEval } from "./global-eval";
+
+// The libdeno functions are moved so that users can't access them.
+type MessageCallback = (msg: Uint8Array) => void;
+interface Libdeno {
+  recv(cb: MessageCallback): void;
+
+  send(msg: ArrayBufferView): null | Uint8Array;
+
+  print(x: string): void;
+
+  mainSource: string;
+  mainSourceMap: RawSourceMap;
+}
+
+const window = globalEval("this");
+export const libdeno = window.libdeno as Libdeno;