render/vulkan: switch to timeline semaphores

Up until now we were using a VkFence for GPU-to-CPU
synchronization. This has some limitations that become a blocker
when trying to have multiple command buffers in flight at once
(e.g. for multi-output). It's desirable to implement a command
buffer pool [1], but VkFence cannot be used to track command buffer
completion for individual subpasses.

Let's just switch to timeline semaphores [2], which fix this issue,
make synchronization a lot more ergonomic and are a core Vulkan 1.2
feature.

[1]: https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/3802
[2]: https://www.khronos.org/blog/vulkan-timeline-semaphores

render/vulkan/vulkan.c

@@ -424,6 +424,7 @@ struct wlr_vk_device *vulkan_device_create(struct wlr_vk_instance *ini,
 		VK_EXT_EXTERNAL_MEMORY_DMA_BUF_EXTENSION_NAME,
 		VK_EXT_QUEUE_FAMILY_FOREIGN_EXTENSION_NAME,
 		VK_EXT_IMAGE_DRM_FORMAT_MODIFIER_EXTENSION_NAME,
+		VK_KHR_TIMELINE_SEMAPHORE_EXTENSION_NAME, // or vulkan 1.2
 	};
 	size_t extensions_len = sizeof(extensions) / sizeof(extensions[0]);
 
@@ -464,8 +465,13 @@ struct wlr_vk_device *vulkan_device_create(struct wlr_vk_instance *ini,
 		.pQueuePriorities = &prio,
 	};
 
+	VkPhysicalDeviceTimelineSemaphoreFeaturesKHR timeline_features = {
+		.sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_TIMELINE_SEMAPHORE_FEATURES_KHR,
+		.timelineSemaphore = VK_TRUE,
+	};
 	VkDeviceCreateInfo dev_info = {
 		.sType = VK_STRUCTURE_TYPE_DEVICE_CREATE_INFO,
+		.pNext = &timeline_features,
 		.queueCreateInfoCount = 1u,
 		.pQueueCreateInfos = &qinfo,
 		.enabledExtensionCount = extensions_len,
@@ -482,6 +488,7 @@ struct wlr_vk_device *vulkan_device_create(struct wlr_vk_instance *ini,
 
 	load_device_proc(dev, "vkGetMemoryFdPropertiesKHR",
 		&dev->api.getMemoryFdPropertiesKHR);
+	load_device_proc(dev, "vkWaitSemaphoresKHR", &dev->api.waitSemaphoresKHR);
 
 	// - check device format support -
 	size_t max_fmts;