Allow binds and unbinds to be used at the same time in the signal connection dialog.

[Macksaur]

Fixes #98686 and behaves like source_signal.connect(target_function.bind(args).unbind(n)).

Enables the red highlighted options:

[quinnyo]

This seems OK to me, it works.

I am not intimate with the Callable code (which is being called into) but the changes here don't seem to be affecting how each of those interactions work in a significant way.

The significant changes being made here remove the strict (perhaps overly-defensive?) mutual exclusion constraint on 'bind' and 'unbind'.

For the record, the 'if unbind then no bind' logic looks like the result of taking the two terms at face value as English words. Which is understandable, but is not, in my understanding, the correct behaviour.

I will mention that #102007 occurs in the CI build for this PR that I tested (as well as the official builds), which did limit testing in a very minor way. I don't think that should change anything for this PR, but I also don't know what will come of that issue, so I mention it for completeness.

[dalexeev]

behaves like source_signal.connect(target_function.bind(args).unbind(n))

This is correct, see the comment for reference. Any sequence of bind() and unbind() calls can be reduced to the form .bind(...).unbind(...). (But I didn't look at the code, just noted that the idea is correct. I would like to review this later if I find free time.)