emoji_codes: Replace JS module with JSON module.

webpack optimizes JSON modules using JSON.parse("{…}"), which is
faster than the normal JavaScript parser.

Update the backend to use emoji_codes.json too instead of the three
separate JSON files.

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

static/js/hotkey.js

@@ -1,3 +1,5 @@
+const emoji_codes = require("../generated/emoji/emoji_codes.json");
+
 function do_narrow_action(action) {
     action(current_msg_list.selected_id(), {trigger: 'hotkey'});
     return true;