iris: Handle vertex shader with window space position
Iris advertises support for PIPE_CAP_TGSI_VS_WINDOW_SPACE_POSITION so let's actually implement it.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110657
Due to an influx of spam, we have had to impose restrictions on new accounts. Please see this wiki page for instructions on how to get full permissions. Sorry for the inconvenience.
Iris advertises support for PIPE_CAP_TGSI_VS_WINDOW_SPACE_POSITION so let's actually implement it.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110657