Provide thread- and thread method-based synchronization.

Notify is an overridden procedure in TIdThread that allows access to the thread-based synchronization and notification mechanism in Indy, and also provides a mechanism to allow the thread to perform notifications for the thread or a thread method.

When the thread-based variant is called, Notify adds the TIdSync instance in ASync to the global notification list in GNotifyThread. When the thread method-based variant is called, Notify calls the previous version using a TIdSyncMethod instance created for the thread method in AMethod.