layers: Special-case threading GetSwapchainImages

This API is a special-case for the code-gen in that it sometimes
returns an array of images. These do not need to be counted by
start/finishReadObject and so were moved into the non-generated
part of the layer source.

Change-Id: Iaaab9143abadbf025b5f3c118aa26dae3c6f1bec
diff --git a/scripts/threading_generator.py b/scripts/threading_generator.py
index fc9174b..97d7df0 100644
--- a/scripts/threading_generator.py
+++ b/scripts/threading_generator.py
@@ -383,6 +383,7 @@
             'vkCreateDebugReportCallbackEXT',
             'vkDestroyDebugReportCallbackEXT',
             'vkAllocateDescriptorSets',
+            'vkGetSwapchainImagesKHR',
         ]
         if name in special_functions:
             decls = self.makeCDecls(cmdinfo.elem)