update vulkan.h for multi-level command buffers (V121)

With minimal changes to keep everything building and functioning.
diff --git a/layers/screenshot.cpp b/layers/screenshot.cpp
index 313bb72..8a968e6 100644
--- a/layers/screenshot.cpp
+++ b/layers/screenshot.cpp
@@ -144,6 +144,7 @@
         VK_STRUCTURE_TYPE_CMD_BUFFER_CREATE_INFO,
         NULL,
         deviceMap[device]->queueNodeIndex,
+        VK_CMD_BUFFER_LEVEL_PRIMARY,
         0
     };
     const VkCmdBufferBeginInfo cmdBufferBeginInfo = {