Introduced the Collection.addMany method and Collection.change event

[mlewand]

Suggested merge commit message (convention)

Feature: Introduced the Collection.addMany() method for adding multiple items in a single call. Closes #7627.

Feature: Introduced the Collection.change event. See #7627.

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Additional information

With this I was also able to simplify DocumentColorCollection by using new change event.

clear() method uses almost the entire remove() logic except that it must not fire change for each removal. Thus I extracted a private base of remove() that can be reused in both cases.

[jodator]

Implementation is OK (only one left over found) 👍

However I'd duplicate tests for add() and addMany() to document the feature we want not to test the implementation we have now.