zink: lower smooth-lines if not supported

zink: lower smooth-lines if not supported

This implements line-smoothing the same way as the draw-module does,
except using a geometry shader instead of a CPU pass.

Ideally, this should be enabled either by checking for the various
smooth-line caps, or by a DRIconf setting.

Unfortunately, RADV doesn't support he smooth-lines features, and we
don't want to force it down a pessimistic shader-key code-path. So that
plan is out the window for now.

While DRIconf is also neat, it's a bit of work to wire up, and we don't
really know of any real-world applications who would need this yet. So,
for now, let's just unconditionally enable is on the IMG proprietary
driver, which is going to need this for sure.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19847>