Rails New: Only add browser restrictions when using importmap

This commit changes the generator for new Rails applications to only add:

```ruby
allow_browser versions: :modern
```

If the application is generated with `--javascript=importmap`. This is
the default, so this PR does not change anything for people that do not
override the JavaScript option.

Author: moonglum

railties/CHANGELOG.md

@@ -104,4 +104,8 @@
 
     *Petrik de Heus*
 
+*   Only add browser restrictions for a new Rails app when using importmap.
+
+    *Lucas Dohmen*
+
 Please check [8-0-stable](https://github.com/rails/rails/blob/8-0-stable/railties/CHANGELOG.md) for previous changes.

railties/lib/rails/generators/rails/app/templates/app/controllers/application_controller.rb.tt

@@ -1,11 +1,9 @@
 class ApplicationController < ActionController::<%= options.api? ? "API" : "Base" %>
-<%- unless options.api? -%>
+<%- if using_importmap? -%>
   # Only allow modern browsers supporting webp images, web push, badges, import maps, CSS nesting, and CSS :has.
   allow_browser versions: :modern
-<%- if using_importmap? -%>
 
   # Changes to the importmap will invalidate the etag for HTML responses
   stale_when_importmap_changes
 <% end -%>
-<% end -%>
 end