Use toolbar item factory for debug button

[fcollonval]

One additional comment I forgot in the review. The new button should be using the new toolbar customization feature.

See for example

@fcollonval
This requires a lot of changes as the button currently is embedded inside the handler, I will add this change to a separate PR. I have made all the other changes as per your suggestions.

Originally posted by @3coins in #10727 (comment)