Assign window.Turbo in @hotwired/turbo-rails/index

With the changes made in the prior commit to pass CI merged, the fact
that Turbo and Turbo Rails somehow have differing references to `Turbo`
and `window.Turbo`.

This commit reverts the test harness change that sets `window.Turbo`,
and instead assigns that value as part of the
`@hotwired/turbo-rails/index` module:

```diff
-import { Turbo } from "@hotwired/turbo-rails"
-
-window.Turbo = Turbo
+import "@hotwired/turbo-rails"
```

app/assets/javascripts/turbo.js

@@ -4810,7 +4810,7 @@ window.Turbo = Turbo;
 
 start();
 
-var turbo_es2017Esm = Object.freeze({
+var Turbo$1 = Object.freeze({
   __proto__: null,
   FetchEnctype: FetchEnctype,
   FetchMethod: FetchMethod,
@@ -4979,6 +4979,8 @@ function isBodyInit(body) {
   return body instanceof FormData || body instanceof URLSearchParams;
 }
 
+window.Turbo = Turbo$1;
+
 addEventListener("turbo:before-fetch-request", encodeMethodIntoRequestBody);
 
 var adapters = {
@@ -5514,4 +5516,4 @@ var index = Object.freeze({
   getConfig: getConfig
 });
 
-export { turbo_es2017Esm as Turbo, cable };
+export { Turbo$1 as Turbo, cable };

app/javascript/turbo/index.js

@@ -8,4 +8,6 @@ export { cable }
 
 import { encodeMethodIntoRequestBody } from "./fetch_requests"
 
+window.Turbo = Turbo
+
 addEventListener("turbo:before-fetch-request", encodeMethodIntoRequestBody)

test/dummy/app/javascript/application.js

@@ -1,4 +1,2 @@
 // Configure your import map in config/importmap.rb. Read more: https://github.com/rails/importmap-rails
-import { Turbo } from "@hotwired/turbo-rails"
-
-window.Turbo = Turbo
+import "@hotwired/turbo-rails"

yarn.lock

@@ -206,9 +206,9 @@ hasown@^2.0.0:
   dependencies:
     function-bind "^1.1.2"
 
-"idiomorph@git+https://github.com/basecamp/idiomorph.git#rollout-build":
+"idiomorph@https://github.com/basecamp/idiomorph#rollout-build":
   version "0.0.8"
-  resolved "git+https://github.com/basecamp/idiomorph.git#e906820368e4c9c52489a3336b8c3826b1bf6de5"
+  resolved "https://github.com/basecamp/idiomorph#e906820368e4c9c52489a3336b8c3826b1bf6de5"
 
 is-core-module@^2.13.0:
   version "2.13.1"