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

CHANGELOG.md

@@ -67,7 +67,7 @@ Bottom level categories:
         - `tan`
         - `tanh`
 - Eager release of GPU resources comes from device.trackers. By @bradwerth in [#5075](https://github.com/gfx-rs/wgpu/pull/5075)
-- Added `InstanceFlags::GPU_BASED_VALIDATION`, which enables GPU-based validation for shaders. This is currently only supported on the DX12 back end; other platforms ignore this flag, for now.
+- Added `InstanceFlags::GPU_BASED_VALIDATION`, which enables GPU-based validation for shaders. This is currently only supported on the DX12 and Vulkan back ends; other platforms ignore this flag, for now.
   - This has been added to the set of flags set by `InstanceFlags::debugging` and `InstanceFlags::from_build_config`. If you notice your graphics workloads running more slowly, this may be the culprit.
   - As with other instance flags, this flag can be changed in calls to `InstanceFlags::with_env` with the new `WGPU_GPU_BASED_VALIDATION` environment variable.
 

wgpu-hal/src/vulkan/instance.rs

@@ -756,6 +756,15 @@ 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(&[vk::ValidationFeatureEnableEXT::GPU_ASSISTED]);
+            if desc
+                .flags
+                .intersects(wgt::InstanceFlags::GPU_BASED_VALIDATION)
+            {
+                create_info = create_info.push_next(&mut gpu_assisted_validation);
+            }
+
             unsafe {
                 profiling::scope!("vkCreateInstance");
                 entry.create_instance(&create_info, None)