Blender Git Loki

Fix T88812: Child Windows on Vertical Monitors

This patch improves the positioning of child windows when on monitors
that are arranged vertically (any above any other). When calculating a
window position in Ghost coordinates from GL coordinates we were using
monitor height, which can give incorrect values when desktop is taller
than any single monitor. So use desktop height instead.

See D10637 for more details and examples.

Differential Revision: https://developer.blender.org/D10637

Reviewed by Brecht Van Lommel