layers: Update Valid Usage enums (VL-70)

Reviewed the following 5 files' invocation of log_msg()
for opportunities to update for Valid Usage enums.
layers/threading.h
layers/vk_layer_logging.h
layers/descriptor_sets.cpp
layers/swapchain.cpp
layers/unique_objects.cpp

Split some composite checks apart, to better match the meaning of
individual VUs.

Added VU enums to a new file, and expanded the stats collection
script to include the new file.

Changed some placeholder uses of msgCode=="0" to
"VALIDATION_ERROR_UNDEFINED".
(0 is the value of the enum VALIDATION_ERROR_00000 which was misleading)

When Valid Usage enums were referenced, also updated the VU database.

Tweak #include order for Windows, to undo clang-format reordering.

Completes Jira task VL-70.

Change-Id: I550922b194e733f41316ae493098f70a54cbd64e
diff --git a/layers/vk_validation_stats.py b/layers/vk_validation_stats.py
index 9019aab..132f46c 100755
--- a/layers/vk_validation_stats.py
+++ b/layers/vk_validation_stats.py
@@ -49,7 +49,8 @@
 'descriptor_sets.cpp',
 'parameter_validation.cpp',
 'object_tracker.cpp',
-'image.cpp'
+'image.cpp',
+'swapchain.cpp'
 ]
 header_file = 'vk_validation_error_messages.h'
 # TODO : Don't hardcode linux path format if we want this to run on windows