refactor(ui5-li): selected property changed to private

[yanaminkova]

The selected property of the ui5-li has been redefined within the class where it is actively utilized. Despite this change, it remains accessible to all components that rely on it.

Related to #8461, #7887

[nnaydenow]

add declare keyword in front of the places where we only want to change the documentation

[nnaydenow]

FYI @MapTo0

[dobrinyonkov]

Related to #9022

[yanaminkova]

add declare keyword in front of the places where we only want to change the documentation

We only need to update the documentation for the ui5-li-notification and ui5-li-notification-group components to remove the selected property. The documentation for all other components should remain unchanged.
Is the declare statement still required in this scenario?

[tsanislavgatev]

@dobrinyonkov @yanaminkova
We've merged: #8871
We inherit ListItemBase and document the selected property as unusable in our case.
Can you please delete our documentation of the selected property in the MenuSeparator component, as the only reason to document it is because of the inheritance?

[kineticjs]

So my understanding is that we define the "select" property in the base class only (i.e in ListItemBase) and then declare it as inherited property in the subclasses where it makes sense to use it.. In the remaining places (MenuSeparator) no mentioning (i.e. no declaration/definition) of the "select" property. Seems coherent, so approving...

Review addressed