Better abstractions in widget operations

Can we ensure that we don't leak abstractions here? Technically, the WidgetOperationSaga should be agnostic to the widget being deleted. Since the tab widget has special handling, we should have a function called `deleteWidget` in the `BaseWidget` class with an empty implementation. If any widget requires a special handling, the specific widget should override it's implementation of the `delete` function to fire the specific event.

_Originally posted by @mohanarpit in https://github.com/appsmithorg/appsmith/pull/3218#discussion_r582884240_