If the [`action_text.helper` initializer][0] runs after
`ActionController::Base` has been loaded, but before the
`rails-html-sanitizer` gem has been `require`d, then the reference to
the constant `Rails::Html` in the body of the
`ActionText::ContentHelper` module raises an `uninitialized constant`
exception.
[0]: 2170338239/actiontext/lib/action_text/engine.rb (L31-L35)
Failing test before the ActionText::RichText change:
```
Error:
ActionText::ModelTest#test_embed_extraction_only_extracts_file_attachments:
ArgumentError: Could not find or build blob: expected attachable, got #<ActionText::Attachables::RemoteImage:0x00007fb0259fef70 @url="http://example.com/cat.jpg", @content_type="image", @width=nil, @height=nil>
```
