Define jQuery object in separate file to support esbuild (#3571)

* Import jQuery in separate file to avoid hoisted variables

* Add blank line for consistency

* Split lines for assignment

* Make option_name mutable to overcome frozen_string_literal

* Return to one-liner init

* Remove unary operator

Author: wayc

src/rails_admin/base.js

@@ -1,6 +1,6 @@
 import Rails from "@rails/ujs";
 import "@hotwired/turbo-rails";
-import jQuery from "jquery";
+import "./jquery";
 import "./vendor/jquery_nested_form";
 import "bootstrap";
 
@@ -27,4 +27,3 @@ import "./ui";
 import "./widgets";
 
 Rails.start();
-window.$ = window.jQuery = jQuery;

src/rails_admin/jquery.js

@@ -0,0 +1,3 @@
+import jQuery from "jquery";
+
+window.$ = window.jQuery = jQuery;