rhi: vulkan: Enable feature for line polygon mode

Turns out there is a fillModeNonSolid in VkPhysicalDeviceFeatures,
so to be true to the spec we need to enable that when setting the
polygonMode in a QRhiGraphicsPipeline to something other than the
default Fill. This way the validation layer won't bark at us.

Change-Id: I41f561a1796ba1d45229dc20bf1fb7bae3c43f48
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

src/gui/rhi/qrhivulkan.cpp

@@ -635,6 +635,8 @@ bool QRhiVulkan::create(QRhi::Flags flags)
             features.textureCompressionBC = VK_TRUE;
         if (physDevFeatures.geometryShader)
             features.geometryShader = VK_TRUE;
+        if (physDevFeatures.fillModeNonSolid)
+            features.fillModeNonSolid = VK_TRUE;
         devInfo.pEnabledFeatures = &features;
 
         VkResult err = f->vkCreateDevice(physDev, &devInfo, nullptr, &dev);