igl | vulkan | Enable dualSrcBlend

Summary:
Fix a validation error:

```
VUID-VkPipelineColorBlendAttachmentState-dstAlphaBlendFactor-00611(ERROR / SPEC): msgNum: -643335502 - Validation Error: [ VUID-VkPipelineColorBlendAttachmentState-dstAlphaBlendFactor-00611 ] Object 0: handle = 0x270a8eafda0, name = Device: VulkanContext::device_, type = VK_OBJECT_TYPE_DEVICE; | MessageID = 0xd9a77ab2 | vkCreateGraphicsPipelines(): pCreateInfo[0].pColorBlendState.pAttachments[0].dstAlphaBlendFactor uses a dual-source blend factor (18), but this device feature is not enabled. The Vulkan spec states: If the dualSrcBlend feature is not enabled, dstAlphaBlendFactor must not be VK_BLEND_FACTOR_SRC1_COLOR, VK_BLEND_FACTOR_ONE_MINUS_SRC1_COLOR, VK_BLEND_FACTOR_SRC1_ALPHA, or VK_BLEND_FACTOR_ONE_MINUS_SRC1_ALPHA (https://vulkan.lunarg.com/doc/view/1.3.243.0/windows/1.3-extensions/vkspec.html#VUID-VkPipelineColorBlendAttachmentState-dstAlphaBlendFactor-00611)
```

Reviewed By: pixelperfect3

Differential Revision: D49335474

fbshipit-source-id: b331816c0b28d8d06875e5cc4d861a17c7b1bd8b

src/igl/vulkan/VulkanHelpers.c

@@ -302,6 +302,7 @@ VkResult ivkCreateDevice(VkPhysicalDevice physicalDevice,
                          VkDevice* outDevice) {
   assert(numQueueCreateInfos >= 1);
   const VkPhysicalDeviceFeatures deviceFeatures = {
+      .dualSrcBlend = VK_TRUE,
       .multiDrawIndirect = VK_TRUE,
       .drawIndirectFirstInstance = VK_TRUE,
       .depthBiasClamp = VK_TRUE,