Call Embed codes service when previewing

This updates `govspeak_to_admin_html` to call the new service on any
generated HTML, so embed codes are transformed in the live preview.

app/helpers/admin/admin_govspeak_helper.rb

@@ -4,7 +4,8 @@ module Admin::AdminGovspeakHelper
   def govspeak_to_admin_html(govspeak, images = [], attachments = [], alternative_format_contact_email = nil)
     images = prepare_images(images)
     attachments = prepare_attachments(attachments, alternative_format_contact_email)
-    wrapped_in_govspeak_div(bare_govspeak_to_admin_html(govspeak, images, attachments))
+    html = ContentBlockManager::FindAndReplaceEmbedCodesService.call bare_govspeak_to_admin_html(govspeak, images, attachments)
+    wrapped_in_govspeak_div(html)
   end
 
   def govspeak_edition_to_admin_html(edition)

test/unit/app/helpers/admin/admin_govspeak_helper_test.rb

@@ -121,4 +121,14 @@ class Admin::AdminGovspeakHelperTest < ActionView::TestCase
       assert_equivalent_html "<div class=\"govspeak\">#{contact_html}</div>", govspeak_to_admin_html(input)
     end
   end
+
+  test "should call the embed codes helper" do
+    input = "Here is some Govspeak"
+    expected = "Expected output"
+    ContentBlockManager::FindAndReplaceEmbedCodesService.expects(:call).with(
+      bare_govspeak_to_admin_html(input, [], []),
+    ).returns(expected)
+
+    assert_equivalent_html "<div class=\"govspeak\">#{expected}</div>", govspeak_to_admin_html(input)
+  end
 end