Export StreamActions as property of window.Turbo

This was removed in #1049
but it's still used in the turbo-rails test suite.

https://github.com/hotwired/turbo-rails/blob/c3ca7009c0759563ec65ecf1bc60a9af1ff33728/test/system/broadcasts_test.rb#L137

src/core/index.js

@@ -3,11 +3,12 @@ import { PageRenderer } from "./drive/page_renderer"
 import { PageSnapshot } from "./drive/page_snapshot"
 import { FrameRenderer } from "./frames/frame_renderer"
 import { FormSubmission } from "./drive/form_submission"
+import { StreamActions } from "./streams/stream_actions"
 import { fetch } from "../http/fetch"
 
 const session = new Session()
 const { cache, navigator } = session
-export { navigator, session, cache, PageRenderer, PageSnapshot, FrameRenderer, fetch }
+export { navigator, session, cache, PageRenderer, PageSnapshot, FrameRenderer, StreamActions, fetch }
 
 /**
  * Starts the main session.

src/index.js

@@ -7,7 +7,6 @@ import * as Turbo from "./core"
 window.Turbo = Turbo
 Turbo.start()
 
-export { StreamActions } from "./core/streams/stream_actions"
 export * from "./core"
 export * from "./elements"
 export * from "./http"