Re-add indirect execution to vulkan downlevel flags (#3319)

Closes #3318

Author: cwfitzgerald

wgpu-hal/src/vulkan/adapter.rs

@@ -327,7 +327,8 @@ impl PhysicalDeviceFeatures {
             | Df::DEPTH_TEXTURE_AND_BUFFER_COPIES
             | Df::WEBGPU_TEXTURE_FORMAT_SUPPORT
             | Df::BUFFER_BINDINGS_NOT_16_BYTE_ALIGNED
-            | Df::UNRESTRICTED_INDEX_BUFFER;
+            | Df::UNRESTRICTED_INDEX_BUFFER
+            | Df::INDIRECT_EXECUTION;
 
         dl_flags.set(Df::CUBE_ARRAY_TEXTURES, self.core.image_cube_array != 0);
         dl_flags.set(Df::ANISOTROPIC_FILTERING, self.core.sampler_anisotropy != 0);