Desktop designer commits once per selected event handler and re-derives subclass events per control

Adding several event handlers at once in the desktop Window designer runs the full edit cycle once per selected event: each handler gets its own source flush, recompile trigger, member-list rebuild, view switch, and undo step. Selecting all of a control's events therefore freezes the IDE repeatedly and produces one undo step per handler. Projects that use custom control subclasses also pay growing compile-preparation cost as windows add more instances of those subclasses, because the subclass event catalogue is re-derived from the class sources for every control instance.

Expected: adding a batch of handlers completes as one fast, single undo step, and compile preparation stays flat as windows grow.