Restore PropertyChangeListener registration (#4415)

* Restore LoggerContext property change listeners

Log4j Core 2 consumers such as Micrometer's `Log4j2Metrics` register a
`java.beans.PropertyChangeListener` on `LoggerContext` to learn about
reconfiguration, and fail with a `NoSuchMethodError` against 3.x since
`addPropertyChangeListener` was removed.

Restore `PROPERTY_CONFIG`, `addPropertyChangeListener` and
`removePropertyChangeListener` as deprecated methods that fire the same
events as in 2.x. The `java.beans` types are confined to a lazily created
helper and `java.desktop` stays optional, so only callers of the
deprecated methods need that module.

* Add changelog entry for property change listeners