ExpandableListItem: Some portings and code improvements
Take null actions into account, and port to Qt 6 list properties
In Qt 6 list properties can be treated as Array-like objects directly. And also actions in the list may be (or become) null, so that should be guarded accordingly.
Fix up example in docs
Port from context properties to ComponentBehavior: Bound
Because Explicit is better than implicit. Zen of Python, anyone?