feat(vulkan): enable GPU-based validation for Vulkan backend

Logic for doing this was sourced from page 3 of [LunarG's guide], with
the following section stack:

* Activating GPU-Assisted Validation
    * Enabling and Specifying Options with the Programmatic Interface

[LunarG's guide]: https://www.lunarg.com/wp-content/uploads/2019/02/GPU-Assisted-Validation_v3_02_22_19.pdf

wgpu-hal/src/vulkan/instance.rs

@@ -756,6 +756,11 @@ impl crate::Instance<super::Api> for super::Instance {
                 create_info = create_info.push_next(vk_create_info);
             }
 
+            let mut gpu_assisted_validation = vk::ValidationFeaturesEXT::builder()
+                .enabled_validation_features(gpu_assisted_validation)
+                .build();
+            create_info = create_info.push_next(&mut gpu_assisted_validation);
+
             unsafe {
                 profiling::scope!("vkCreateInstance");
                 entry.create_instance(&create_info, None)