zink: filled quad emulation gs generation function

zink: filled quad emulation gs generation function

This change adds a function to generate a geometry shader that will take a quad
as an input (passed as a line strip with adjacency because quads are not
available as an input primitives for GS) and generate a triangle strip.

This can be used to emulate the quad primitive.

Acked-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21238>