dragTo should trigger mouseOver before drop

[das-peter]

Just fiddled with the Drag n Drop testing and came across an issue when testing it with ExtJs e.g. https://docs.sencha.com/extjs/4.2.2/extjs-build/examples/tree/custom-drop-logic.html
Dragging works fine - but dropping runs into nothing because the destination event isn't "ready".
I think most dynamic libraries prepare the destination by listening to a hover event - which currently isn't triggered when dragging n droping.
However, I think the native browser behavior indeed would trigger a mouse over before a drop event.
Hence the added event before the button up.

Tested with:

Feature: DragNDropTest
    Scenario: DragNDropTest
        Given I go to "https://docs.sencha.com/extjs/4.2.2/extjs-build/examples/tree/custom-drop-logic.html"
        And I wait for "2" seconds
        And I drag "#treeview-1013-record-ext-record-1" to "#treeview-1017-record-ext-record-6 div"

Without the patch it fails, with the patch it works as expected.

---

Found that the mouseover / button up might cause the destination element to be stale.
Added a re-fetch before the final event trigger to avoid that issue.

[uuf6429]

Seems to relate to #408. Let's continue the discussion there.

[uuf6429]

@das-peter the PR I mentioned earlier has now been merged. Could you try your test again with it and see if the issue persists? Thanks.