Vulkan: Finish semantics for what creates spec-const-semantics.

Note: This required adding a new test mode to see the AST for vulkan tests.
This also required reworking some deeper parts of type creation, regarding
when storage qualification and constness is deduced bottom-up or dictated
top-down.

gtests/TestFixture.cpp

@@ -94,7 +94,7 @@ EShMessages DeriveOptions(Source source, Semantics semantics, Target target)
         case Semantics::OpenGL:
             break;
         case Semantics::Vulkan:
-            result = static_cast<EShMessages>(result | EShMsgVulkanRules);
+            result = static_cast<EShMessages>(result | EShMsgVulkanRules | EShMsgSpvRules);
             break;
     }