Fix preventing layer from pushing itself

Add _private QtObject back and comment why

Code review changes 1

Handle checked status with exclusive groups

Honor checkable state of Action

I am going to commit some unit tests for this so I don't miss something else :)

• Rename variable and add comment

Just following up on this change review—it all looks good to me. Can we merge it in?

I think there's issues with this. I had assumed it is fine to load static plugins regardless of from where, but in my testing there are issues so I think this needs to be an "either or" scenario instead of allowing static/dynamic plugins to intermix.

It appears all the sources which reference the export header have an appropriate guard on them:

Ah, I'll take a closer look.