Bug 1461708 - part 8: Make EventStateManager handle middle click paste as a default action of mouseup event r=smaug

This patch makes EventStateManager handle middle click paste as a default
action.

Unfortunately, we cannot remove the call of HandleMiddleClickPaste() in
EditorEventListener because it's important to consume middle click event
before any elements in the editor.  For example, if clicked HTMLEditor has
non-editable <a href> element, middle click event needs to be handled by the
editor rather than contentAreaUtils which handles click events of <a href>
elements.  The cause of this kind of issues is, any click event handlers
which handle non-primary button events still listen to "click" events.
Therefore, this patch makes HandleMiddleClickPaste() do nothing if the mouseup
event is fired on an editor.

Differential Revision: https://phabricator.services.mozilla.com/D7855

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extra : moz-landing-system : lando