Allow layers to enable VK_TOOL_PURPOSE_DEBUG_MARKERS_BIT_EXT in vkGetPhysicalDeviceToolPropertiesEXT()

Some game engines (e.g. UE5) will emit debug markers if `vkGetPhysicalDeviceToolPropertiesEXT()` returns `VK_TOOL_PURPOSE_DEBUG_MARKERS_BIT_EXT`, so we should support this to prevent users needing to configure via a separate mechanism.