Update allowed changes on classes in BC promise

[chalasr]

I see some points that could be good to update in the document:

• When an element is flagged @final or is final, some "no" in the list of allowed changes ("Changing classes") become "yes", such as adding/removing argument, more generally all changes that could break when extending the element
• An argument can be added to a public method (depending on some conditions) using func_get_args/func_num_args.

WDYT?
/cc @GuilhemN

[GuilhemN]

When an element is flagged @Final or is final, some "no" in the list of allowed changes ("Changing classes") become "yes", such as adding/removing argument, more generally all changes that could break when extending the element

👍, same applies for final methods.
I would change that either by add a reference to a note (eg [6]) or reword No to No, unless final where needed.

An argument can be added to a public method (depending on some conditions) using func_get_args/func_num_args.

👍, in fact it would be great to specify the bc layer we use for each kind of change (removing a class, removing a property, etc).

[theofidry]

Careful though, a class that have been flagged as @final cannot be changed yet and are still subject to the same BC promises as before. It's simply like for the @deprecated, they will change in the future.

[GuilhemN]

see #7597