js: Convert static/js/floating_recipient_bar.js to ES6 module.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

static/js/compose_fade.js

@@ -1,6 +1,7 @@
 import _ from "lodash";
 
 import * as compose_state from "./compose_state";
+import * as floating_recipient_bar from "./floating_recipient_bar";
 import * as message_viewport from "./message_viewport";
 import * as people from "./people";
 import * as rows from "./rows";