[pointercapture] wrong target element on pointerup (mouse events mapping)

[seb-pereira]

When pointers are mapped against native mouse events and pointer capture is enabled, releasing the button outside the captured element cause the pointerup event to be targeted to the element beneath the mouse pointer, instead of the captured element.

[cjolif]

would have been good to have a test case committed as well so we notice if we regress on that later?

[seb-pereira]

Tests are under development (ref #6). Test cases related to newly fixed issues will be included as appropriate.