layers: Move platform WSI extension checks from swapchain to PV

We want to do all extension checks in PV-- we'll return a good FP for
anything we recognize, and complain upfront if the appropriate extension
wasn't enabled.

Signed-off-by: Chris Forbes <chrisforbes@google.com>
diff --git a/layers/parameter_validation_utils.h b/layers/parameter_validation_utils.h
index 099018e..be27cbf 100644
--- a/layers/parameter_validation_utils.h
+++ b/layers/parameter_validation_utils.h
@@ -58,6 +58,9 @@
                           // the device
     FAILURE_RETURN_CODE,  // A Vulkan return code indicating a failure condition
                           // was encountered.
+    EXTENSION_NOT_ENABLED,// An extension entrypoint was called, but the required
+                          // extension was not enabled at CreateInstance or
+                          // CreateDevice time.
 };
 
 struct GenericHeader {