Blender Git Loki

Viewport: change Z key to shading pie menu to switch mode, X-ray and overlays.

This lets us do the most common shading switching with one shortcut. We keep
alt+Z and shift+Z for quickly toggling to lookdev and rendered mode and back,
it's debatable which settings deserve a dedicated shortcut like this.

The downside is that switching X-ray is a little slower, and that there is
some risk of accidentally going to lookdev or rendered mode which can be slow
to cancel.