MouseClick event

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A common want is to be able to react to a press and a release on the same collision entity. To do this we'd need to track the LastMousePress just like we track the last mouse event, and on release, if both press and release collide with an entity trigger a MouseClick on the entity.

This would mean that you could press on an entity, drag off of the entity, drag back on, and release to click, but this seems acceptable.

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This is done in develop.