Bundle cursor wrapping algorithms from PageView and ThumbnailListPrivate

This bundles mouse cursor wrapping algorithms from PageView::... and ThumbnailListPrivate::mouseMoveEvent() GuiUtils::CursorWrapHelper. This simplifies the code in PageView::mouseMoveEvent(), which is basically concerned about more important stuff than cursor wrapping.

GuiUtils::CursorWrapHelper::wrapCursor() returns only whether the cursor was moved. This is intended, because Qt can not guarantee how much or whether at all the cursor is repositioned.

As far as I could test it, it also works on translated hiDPI screens.

Suggested commit message

Unify cursor wrapping code in ThumbnailList and PageView

Create a new class GuiUtils::CursorWrapHelper, which bundles
mouse cursor wrapping algorithms from PageView and ThumbnailListPrivate::mouseMoveEvent()
in a class.

PageView::mouseMoveEvent() now only calls GuiUtils::CursorWrapHelper::wrapCursor(),
which simplifies the remaining code.