nir: Rename nir_is_per_vertex_io to nir_is_arrayed_io

VS outputs are "per vertex" but not the kind of I/O we want to match
with this helper.  Change to a name that covers the "arrayness"
required by the type.

Name inspired by the GLSL spec definition of arrayed I/O.

Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10493>

src/compiler/spirv/vtn_variables.c

@@ -1884,7 +1884,7 @@ vtn_create_variable(struct vtn_builder *b, struct vtn_value *val,
       }
 
       struct vtn_type *per_vertex_type = var->type;
-      if (nir_is_per_vertex_io(var->var, b->shader->info.stage))
+      if (nir_is_arrayed_io(var->var, b->shader->info.stage))
          per_vertex_type = var->type->array_element;
 
       /* Figure out the interface block type. */