Add decorations to structs with buffer references

The containsPhysicalStorageBufferOrArray function now handles struct
types correctly, checking their contents recursively for buffer
reference types. As a result, OpVariables containing structs that have
members that are buffer references now have the appropriate
AliasedPointer or RestrictPointer decoration as per the spec.

Fixes #3188

Test/spv.bufferhandle8.frag

@@ -27,6 +27,8 @@ layout(set=0, binding=0) buffer T3 {
   Blah Bindings[];
 } t3;
 
+
 void main() {
+    Blah x = t3.Bindings[2];
     t3.Bindings[0] = t3.Bindings[1];
 }