window: Defer focus setting until after paint

window: Defer focus setting until after paint

Commit 3dbf5038fab8eb0d8c11 tried to defer focus changes
until after rendering is done. But it failed to do so, since
the toplevel ::render handler is still before rendering of
popups that are attached to that toplevel. To do this
properly, we need to do it in the AFTER_PAINT frame clock
phase.

Fixes: #3725