QRegion::contains(QRect) does not return if the region contains the rect

While the documentation does say that `QRegion::contains(QRect)` tests for overlap, that does not make the API any less error prone, and noone would ever expect to need to read the documentation for such a seemingly completely straight forward method!

In KWin I'm now using `(region & rect) == rect` as the workaround to this problem, but this method should really be deprecated and replaced with `intersects(QRect)`.