Event handling doesn't support AnnouncementSet

[tinchodias]

Reproduce with:

BlElement new
	addEventHandlerOn: BlClickEvent, BlMouseDownEvent, BlMouseUpEvent
	do: [ ].

to get a "Instance of AnnouncementSet did not understand #enableIn:"

In Pharo12.

[tinchodias]

For the record, I did a first try and failed to fix it. I share the code below.

I created this test in BlEventTest:

testAnnouncementSet

	| element events |
	events := OrderedCollection new.

	element := BlElement new.
	element
		addEventHandlerOn: BlClickEvent, BlMouseMoveEvent
		do: [ :anEvent | events add: anEvent class ].
	
	BlSpace
		simulateMouseMoveInside: element;
		simulateClickOn: element button: BlMouseButton primary;
		simulateMouseDownOn: element; "should be ignored"
		simulateClickOn: element button: BlMouseButton secondary.

	self assert: events asArray equals: { BlMouseMoveEvent. BlClickEvent. BlClickEvent }

and created this extension in AnnouncementSet:

enableIn: aBlElementEventDispatcher

	^ self do: [ :each | each enableIn: aBlElementEventDispatcher ]