draw_state: Add validation extension record

To make things easier for applications the validation
layers will advertise support for two extensions.
The named extension (i.e. DRAW_STATE) is used if the
app only wants to enable this specific layer / extension.
If an app wants to enable all Validation layers they
simply include all VkExtensionProperties who's name is
"Validation". This patch adds this extension to this
layer.
diff --git a/layers/draw_state.cpp b/layers/draw_state.cpp
index 4955cf1..4b76f05 100644
--- a/layers/draw_state.cpp
+++ b/layers/draw_state.cpp
@@ -1599,13 +1599,19 @@
     uint32_t version;
     const char * const name;
 };
-#define DRAW_STATE_LAYER_EXT_ARRAY_SIZE 1
+#define DRAW_STATE_LAYER_EXT_ARRAY_SIZE 2
 static const VkExtensionProperties dsExts[DRAW_STATE_LAYER_EXT_ARRAY_SIZE] = {
     {
         VK_STRUCTURE_TYPE_EXTENSION_PROPERTIES,
         "DrawState",
         0x10,
         "Sample layer: DrawState",
+    },
+    {
+        VK_STRUCTURE_TYPE_EXTENSION_PROPERTIES,
+        "Validation",
+        0x10,
+        "Sample layer: DrawState",
     }
 };
 
@@ -3088,5 +3094,4 @@
             return NULL;
         return pTable->GetInstanceProcAddr(instance, funcName);
     }
-
 }