sws: Sync with upstream

Changes in this version:
* [Store layout window flags in single variable](valinet/sws@633fb2c)
* [Use external variable to detect if desktop is foreground](valinet/sws@4b9ff84)
* [Fix regression when detecting foreground window changes](valinet/sws@8ab7a45)
* [Draw DWM-like placeholder when window has zero width or height](valinet/sws@764a291)
* [Enforce a minimum size for a window rectangle](valinet/sws@bc8b04e)